Super Tuesday primaries have traditionally been a pivotal point in U.S. presidential nominations. This year it will likely be remembered as the event after which the Republicans turned, all guns blazing, on themselves.

With billionaire Donald Trump having secured his anti-establishment, front-runner status by sweeping up the lion's share of Republican delegates up for grabs last Tuesday, party worthies clearly saw this moment as their last chance to try to stop his divisive, populist juggernaut.

But Republicans delivered a split verdict on Saturday, with Trump and Ted Cruz each taking two contests in the latest round of presidential voting. Trump won Kentucky and Louisiana, while Cruz claimed Kansas and Maine. Florida Senator Marco Rubio was left out in the cold, prompting Trump to call on him to quit the race.

Earlier this week, former Massachusetts governor Mitt Romney, the party's presidential standard bearer in 2012, was first out of the gate with a harsh denunciation of Trump as "a phoney" who is "unfit to be president" and whose "imagination must not be married to real power."

He also called on Republican voters in future primaries to set aside their preferences and vote for the candidate they felt had the best chance of winning that state over Trump, in order to set up a contested convention in the summer.

As the week wore on, one well-funded Republican group filed papers to draft Congressional Speaker Paul Ryan into the White House race, though Ryan, the country's senior elected Republican, said through a spokesman that he had no interest in taking this on. (Romney, when pressed by reporters, also said he could not see himself running again this time.)

David Frum, senior editor at The Atlantic magazine and a former speech writer for President George W. Bush, says although "the probabilities are" that Trump will get the nomination, "it's not all over."

"There are a lot of ways that it could still go wrong for him between now and the convention time in Cleveland," Frum told CBC News Network. "In the next two weeks there's going to be a barrage of anti-Trump advertising."

The most damaging advertising themes against the front-runner, he said, include what's been called the Trump University scandal (New York's attorney general launched a lawsuit in 2013 alleging the school was a phoney scheme that defrauded students of some $40 million); and accusations that Trump doesn't really care about the economic well-being of the people who vote for him.

"Those things have drawn blood," Frum said.

'Mini-Super Tuesday' still to come

Trump's contest tally now stands at 12 wins, including the seven he won on Super Tuesday. Cruz has won six, including his home state of Texas, and Rubio has one, in Minnesota.

Clinton won seven of the 11 Super Tuesday races on the Democrat side, with big margins that put her well ahead of her rival Bernie Sanders. The Democrat races Saturday were also split: Clinton picked up Louisiana while Sanders nabbed wins in Nebraska and Kansas.

Trump and Clinton are now eyeing a slew of primaries and caucuses before the month's over, including the important, so-called mini-Super Tuesday on March 15, where four of the six states on the Republican slate are winner take all.

That's when Cruz and Rubio could make inroads against the Trump tide.

The Florida contest with its winner-take-all 99 delegates could pay off for Rubio as he looks for support in his home state, though the most recent polls showed Trump leading there. The same for Ohio Gov. John Kasich, whose home state will offer up its 66 delegates then.

In the meantime, there are four Republican contests this Tuesday, March 8, including the big industrial state of Michigan, which will undoubtedly be seen as a test of whether Trump can do well among blue collar voters, the so-called Ronald Reagan Democrats who crossed over to the Republican Party back in the 1980s. 

Democrats looking forward 

With Clinton steadfastly maintaining her lead over Sanders in most of the races so far, she is turning her attention to defeating Trump in the Nov. 8 election.

The New York Times reports the Democrats are "building up troves of opposition research" on Trump.

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Hillary Clinton greets supporters as she arrives to address Democrats at her Super Tuesday election night rally in Miami. (Gerarld Herbert/Associated Press)

Democrat pollster Geoff Garin, who was Clinton's chief strategist in 2008, was quoted in Monday's article as saying they're investigating his "temperament" to serve and "whether he can be relied on as a champion for anyone but himself."

As for Trump, even if he continues to do well in the races ahead, political observers say there could be a late-game twist if a brokered national convention materializes to replace the usual celebratory love-in bestowed upon the presumptive nominee.

That scenario, in which no candidate brings a majority of party delegates into July's convention — setting the stage for, possibly, a series of ballots — seems to be one for the history books.

The last truly brokered conventions — which gives the two parties' so-called superdelegates more power to decide the outcome — were in 1948 for the Republicans and 1952 for the Democrats.

Still, rumours persist that there could be a kind of brokered convention this time, complete with backroom deals, arranged by those Republicans not keen on having Trump secure the nomination.

Roger Stone, a political strategist who worked for the party on nine presidential campaigns, and is now a member of the Libertarian Party, writes that party insiders want to stall Trump "short of a majority on the first ballot, since many of the delegates pledged to him would no longer be legally bound to support him on subsequent ballots."

No contest the norm at conventions

Usually the nominee for the parties is a foregone conclusion by the time the conventions are held — on July 18-21 in Cleveland for Republicans and July 25-28 in Philadelphia for the Democrats. A single ballot has been the norm for several decades. 

Following a now venerable tradition, establishing platform normally takes up the first couple of days of the convention, before a roll call for the nominee is held. Votes are called out, as they were registered in the state primaries and caucuses, and then a winner is declared, without further balloting or upsets.

But even though delegates register their votes in the primaries and caucuses, and that support is expected to be declared at the convention, delegates have been known to ignore the rules and vote as they please sometimes.

For instance, there was a vocal revolt during roll call at the 2012 Republican convention that saw Mitt Romney take the nomination. He had a majority of Nevada's committed delegates in first-round balloting, but a number of them ignored party rules on voting and made it clear they were supporting Ron Paul instead.

'Superdelegates' influence still possible

Then there are the so-called superdelegates, who go into the convention without necessarily pledging an allegiance. 

Superdelegates are elected officials, such as state governors and members of Congress, and party administrators who serve as unpledged delegates to the Democratic National Convention

The 2008 book The Party Decides: Presidential Nominations Before and After Reform says these high-ranking party officials can ultimately decide who wins the nomination through various means of influence, as they direct support toward a certain candidate.

Republicans don't call their wildcard delegates superdelegates, but "RNC delegates" appointed from party officials in each state. They, too, are not bound to vote for any candidate once the convention begins.

About seven per cent, or roughly 170 of the 2,472 Republican delegates expected at the convention, are in this category.

The equivalent (superdelegate) figure for the Democrats is about 15 per cent, or just over 700 of the expected 4,763 voting delegates.

Clinton has a far greater share of them than Sanders. But campaign observers say she has been careful not to trumpet that kind of support, in order to avoid any appearance that the party establishment is a larger driving force than the grassroots.