Here's a cheat sheet for the U.S. midterms

With just a few days to go, here's how the U.S. midterm elections work — and how they'll reshape the American political landscape ahead of the next presidential election in 2020.

This fall, Americans choose who controls Congress for the next 2 years

There's a lot at stake in the Nov. 6 U.S. midterm elections. Donald Trump has been on the trail for weeks, campaigning with Republican candidates and making his case to a base of fervent supporters. But Democrats have been pushing back and hope to make gains. (Saul Loeb/AFP/Getty Images)

It's a referendum on U.S. President Donald Trump. It's a chance for Democrats to steer the legislative agenda. It's a test for Republicans wondering if they should embolden their actions and themselves.

Any way you slice it, the U.S. midterm elections will allow voters to significantly change the makeup of Congress about halfway through Trump's four-year term.

In the lead-up to the vote, Democrats tried to keep their campaign message focused on issues like health care, while many Republican hopefuls honed in on the economy. The president seemed at times to have his own agenda, returning over and over to the issue of illegal immigration. 

The outcome of the deeply contentious campaign could reshape the American political landscape ahead of the next general election in 2020. With just a few days to go, here's how the midterm elections work.

When will the midterms happen?

The midterm elections will mostly take place on Nov. 6.

They are national elections, sometimes described as "off-year" elections. The founding fathers of the United States set up a political system of checks involving frequent, rolling American elections in even-numbered years.

House members serve two-year terms, so they run in both "on years" with presidential contests, as well as in off years, without a presidential race, along with one-third of the Senate.

CBC's Keith Boag looks at U.S. President Donald Trump's midterm strategy — and whether it's working:

The way elections are staggered means that an election — either a presidential or a midterm — ends up being held every two years.

Why so often? Because "the founders didn't want politicians to get too comfortable," explained Mark Harkins, a Capitol Hill veteran and senior fellow at Georgetown University's Government Affairs Institute.

The idea is that holding frequent elections reins in potential "unbridled ambitions," he said.

Who's actually on the ballot?

Not the president.

The full 435-seat House of Representatives will be in contention at one time because its members serve a two-year term.

Trump addresses a joint session of Congress in this February 2017 file photo. As the saying goes: 'The party that controls the chamber, controls the agenda.' (J. Scott Applewhite/Associated Press)

The Senate, which has 100 members, works differently. It's on its own cycle because senators serve six-year terms, so only one-third of Senate seats will be up for grabs every two years. This year, 35 Senate seats are in play: 33 senators, plus two special elections.

Aside from Congress, there are 39 state and territorial governorships up for grabs.

Why is the Senate on a different cycle?

Unlike the House, the Senate never stands for election at one time.

The framers of the Constitution purposely designed the Senate "to be more politically insulated," explains Linda Fowler, a professor of government with Dartmouth College.

Are the midterms good for presidents?

Historically, no. It's quite the opposite — a fact that Trump is well aware of at a time when he's unpopular in the polls.

"When you win the presidency, for some reason, you always end up losing the House," Trump said in May at a rally in Nashville.

Trump has also expressed confidence he'll reverse the trend. How many seats in Congress his party wins or loses in the midterms will be a sign of how the populace feels about him and his party's performance.

"Presidents tend to overreach in the first two years, and midterms are a way for the populace to lodge their concerns with the chief executive," Harkins said. "Trump's not on the ballot, so the way they lodge concerns is in the House of Representatives."

In 2010, two years into his first term, Barack Obama's Democrats lost a whopping 63 seats in the House, with the then-president memorably conceding it was a "shellacking."

Bottom line: The party that has control of the White House typically loses seats.

Isn't that good for the Democrats?

If historical trends play out again this year, then yes.

Consider that in nearly every midterm election after the Second World War, from 1946 to 2014, the party occupying the White House ended up suffering net losses of House seats. (The only exceptions were in 1998, when Bill Clinton picked up five Democratic seats, and in 2002, when George W. Bush picked up two seats for his Republicans.)

"Generally speaking, if you're a fan of Republicans and Trump, you'll be nervous," Harkins said. That's because the average net loss for incumbent presidents after the Second World War was 25 House seats and four Senate seats.

As of early November, the House of Representatives had 235 Republicans, 193 Democrats and seven vacant seats.

The number of "pickups" needed for the Democrats to win a majority in the House this year varies depending on whether vacancies are factored in.

Will the Democrats take the Senate?

Republicans have an even slimmer majority in the Senate, where there are 51 Republicans, 47 Democrats and two independents who caucus with the Democrats.

Of the 35 Senate seats up for grabs, just nine are held by Republicans. Democrats have nearly three times the number of seats considered to be must-win, as 26 seats are currently held by senators who caucus with the Democrats.

Some Democratic incumbents, like North Dakota's Heidi Heitkamp, are vulnerable. Another challenge for the party: 10 of the Democratic or left-leaning independents running will be competing in states that Trump carried in the presidential election.

One Senate race people will be watching next week is in Texas, where Democrat Beto O'Rourke is trying to push out high-profile Republican Ted Cruz. 

The long-serving Republican is still the favourite to win, but O'Rourke's bid is drawing a huge amount of attention — and raising massive amounts of money.

CBC's Paul Hunter went to Texas to see how the race was unfolding:

Ahead of Tuesday's vote, most forecasters suggest the Senate changing hands is a long shot.

Not only do Democrats have to defend all their Senate seats, they'll also have to pick up two more by flipping Republican seats to take control.

"It would have to be a real repudiation of the sitting president for the Republicans to give up control of the Senate," Fowler said. "It's not impossible — but it's less likely."

Will the Democrats take the House?

In the last 25 years, the House has changed hands only three times during midterm elections — in 1994, 2006 and 2010. 

Democrats are nevertheless optimistic that they can pick up the 23 seats they need to take control of the House. There's excitement about a possible "blue wave" that could sweep them into the House and the Senate. 

Earlier in the campaign, Keith Boag looked at how Democrats are pushing against the president:

"Political statisticians are putting the odds of Republicans losing control of the House at about 50-50," Fowler said in early July. 

By early November, most forecasts suggested the Democrats have a solid shot at winning the House.

Why care about who controls Congress?

As the saying goes: "The party that controls the chamber, controls the agenda."

Consider this year's backdrop of the Russia investigations, legislative battles over immigration, gun rights and health care. If the Republicans maintain control, expect reinvigorated efforts to dismantle the Affordable Care Act and another swing at trying to get Trump's border wall constructed.

"They may try to find additional tax cuts, to find ways to roll back the regulatory authority of certain agencies using the legislative process instead of the president's executive authority," Harkins said.

A voter cast his ballot during early voting at a library in Nashville. Phil Bredesen, a former Democratic governor of Tennessee, is in the running against a Republican House member, Marsha Blackburn, for a vacant Senate seat. (Drew Angerer/Getty Images)

A Democratic takeover might lead to re-examination of immigration reform, particularly as it pertains to legalizing people who were once protected by the Deferred Action for Childhood Arrivals (DACA) policy, an Obama-era program that shielded from deportation some who came to the U.S. illegally with their parents when they were young children.

While Trump could veto a DACA bill, it might cost him votes among moderate Republicans in the important battleground state of Florida in 2020.

The threat of impeaching Trump could also rise with Democrats in control of the House, as impeachment comes down to a majority vote in the House before being forwarded onto the Senate.

Does Canada have a stake in this?

Of course. Even with the new United States-Mexico-Canada Agreement, there are still outstanding trade issues between the two countries, including the issue of tariffs on steel and aluminum.

Trump justified those tariffs by citing "national security" grounds, so Republican Sen. Bob Corker, a vocal Trump critic, tried to introduce a bipartisan bill to force the president to get congressional approval to enact tariffs on the basis of national security. He was unsuccessful.

Trump and Prime Minister Justin Trudeau have clashed recently over NAFTA negotiations and U.S.-imposed tariffs on Canadian steel and aluminum. (Evan Vucci/Associated Press)

Corker accused Republican leadership of being too afraid to "poke the bear" that is Trump right before the midterms.

If the configuration of Congress changes, one might imagine that the bill would stand a better chance of advancing. Economists would see that as good news for Canada.

Power and Politics looks at what the U.S. midterms mean for Canada:

Americans are headed to the polls to vote in midterm elections, and the outcome could change Canada’s relationship with the U.S. on several key issues. 1:55

Does turnout matter?

Yes. Democrats are worried about a "midterm falloff."

Turnout for the midterms in the U.S. is always much lower than in general elections; it was around 36 per cent of registered voters in 2014.

Registered voters who tend to drop off at the midterms tend to be: lower-income, minorities, less educated, younger, or female. That has traditionally been a problem for the Democratic Party, as older, white voters who give a boost to the Republicans continue to participate in midterm elections in stronger numbers.

Democrats are hoping their female and millennial supporters will be motivated by anger over the Trump administration's actions to contribute to a surge in support at the polls.

What about the Russia probe?

If the Democrats took the House, the Senate, or both, they'd have the instruments of investigatory power smack-dab in the middle of an ongoing probe into Russian meddling in the 2016 presidential election.

"As part of agenda control, investigations are determined by the parties that control the chambers," Fowler said. "But if the Republicans lose one or both chambers, those investigations will become much more aggressive — because it will be Democrats looking to damage President Trump before the 2020 presidential election."

Congressional investigations are serious and each chamber would, by law, have subpoena powers.

"They could, for example, subpoena President Trump's income-tax returns," Fowler said. "I don't think this president fully appreciates how miserable his life could become if his party loses both chambers."

About the Author

Matt Kwong

Reporter

Matt Kwong is a Washington-based correspondent for CBC News. He previously reported for CBC News as an online journalist in New York and Toronto. You can follow him on Twitter at: @matt_kwong

With files from CBC's Lyndsay Duncombe and Jennifer Walter