In her Democratic National Convention speech, Hillary Clinton suggested her record of working "across the aisle" to pass laws would enable her, as president, to break the gridlock in Congress and push through her policy agenda. 

Whether she really believes that or not, at best it seems to be wishful thinking.

"None of her major goals will be accomplished, in all likelihood," said Geoffrey Skelley, a political analyst at the University of Virginia Center for Politics. 

"The country is extremely polarized and Republicans in Congress are going to have zero interest in giving her any kind of win."

If Donald Trump wins in November, Republicans may end up controlling both the executive and legislative branches of government. Yet he, too, would likely face hurdles to implementing key elements of his platform, though he would certainly have an advantage.

Currently, the Republicans hold both houses of the U.S. Congress and it's considered unlikely that the House of Representatives will switch hands in next fall's election, regardless of who wins the presidency. This means that, at best, Clinton can hope for control of the Senate to fall to the Democrats, but she would still be hamstrung by the Republican-controlled House.

Clinton has laid out an ambitious domestic agenda, plans that include passing what would be, according to her, the biggest investment in jobs since the Second World War. She has also pledged to make college tuition-free for the middle class, raise taxes on the wealthiest Americans, raise the federal minimum wage and expand affordable health care.

Campaign 2016 Clinton

Democratic candidate Clinton can hope, at best, for the Senate to switch over to the Democrats if she wins the election. But she would still almost certainly be hamstrung by a Republican-controlled House. (Andrew Harnik/Associated Press)

While there could be room for compromise on smaller issues, such as bipartisan support for criminal justice reform and some tax policy, it would be a struggle for her to pass her big-ticket items through Congress. 

"She won't be able to get most of that laundry list done, and she's savvy enough to know that," said Julian Zelizer, professor of history and public affairs at Princeton University. "Civility, reaching across the aisle, none of that really works. House Republicans are dug in on a lot of domestic issues and that won't have any big effect."

Yet if the Democrats can significantly cut into the Republicans' House majority, some of the more moderate GOP members, who do not follow in lockstep with the party, might be persuaded to throw their support behind watered-down versions of one of Clinton's proposals.

"It's not inconceivable that if the numbers change, that there could be some deal-making," said Matthew Baum, a professor of public policy at Harvard University's John F. Kennedy School of Government. "Those opportunities may be few and far between. But they may be more than zero."

And Clinton would still have executive powers, something U.S. President Barack Obama has wielded, albeit controversially, to bypass Congress.

Conservatives' biggest fear, however, is the ability Clinton would have to fill vacancies on the U.S. Supreme Court, although Republicans would surely put up a fight and attempt to filibuster her nominees. 

Building a wall

On the other hand, a Trump win that maintained the status quo in Congress could mean the passage of some Republican-led policy initiatives. But even if the Republicans retain the Senate, it's unlikely they would have the 60-vote majority needed to shield their legislation from filibuster, meaning that Trump, too, would face hurdles in getting his agenda passed.

Trump has not been as specific on policy initiatives as Clinton. On Monday, he spoke about his economic plan, including his proposal to cut personal and corporate taxes and increase infrastructure spending. (His economic package also includes asking TransCanada to renew its permit application for the Keystone XL pipeline.)

He has been very vocal about his desire to construct a wall along the U.S.-Mexico border to keep out illegal immigrants. And he has also suggested a temporary ban on Muslims coming into the U.S, but has since appeared to soften his stance. 

The former reality TV host has also made waves by saying he wouldn't necessarily honour U.S. obligations to come to the defence of NATO allies, and he has vowed to impose tariffs on Chinese imports and on goods from U.S. companies that have set up plants in Mexico.

Campaign 2016 Trump

Republican candidate Trump, whose election could bring Republicans control of both the executive and legislative branches of government, may also face hurdles to enacting key parts of his platform. (Evan Vucci/Associated Press)

Trump would likely receive Republican congressional support for his plans to cut taxes, but some of his other initiatives, particularly those considered anti-trade, would likely run into strong opposition from the GOP.

The Republicans "won't help him do things that go against their agenda," Zelizer said.

Even his plan to build a wall — assuming that Mexico, despite Trump's assurances, would not pay for it — may be a difficult sell for Republicans, wary of the multi-billion-dollar cost of such a structure.

Although Republicans would oppose his tepid view of NATO, as president, he would have the power to weaken the U.S.'s commitment to its military alliances. 

"He can unilaterally significantly reduce the extent to which the United States lives up to them," Baum said. "He could make a great deal of mischief in that respect."

Zelizer said some Republicans will decide it's better to forge deals with Trump to push forward some kind of agenda because it will be good for the party. 

Yet the tensions are so significant between him and many Republicans, and it's still unclear what his agenda would be, Zelizer said.

"You can imagine him doing things that don't sit well with other Republicans. You could imagine him all of a sudden cutting deals with Democrats. So I think it's kind of an unknown."