Donald Trump. Matthew Busch/Getty Images Tuesday appears to be the best chance Donald Trump's GOP foes have to slow down his path to their party's presidential nomination.

With more than 350 delegates up for grabs in five primary states, the Republican frontrunner is looking to score big wins that could make his march to the nomination almost unstoppable.

Trump victories in Ohio and Florida alone would most likely put him hundreds of delegates ahead of his closest competitor, Sen. Ted Cruz of Texas.

Of the states voting Tuesday — Ohio, Florida, North Carolina, Missouri, and Illinois — Trump led in recent public polls in all of them except Ohio.

Most of the attention is focused on Ohio and Florida, two states where the candidate who gets the largest share of the vote wins all of the state's delegates. The states also provide do-or-die contests for two of Trump's rivals, Gov. John Kasich of Ohio and Sen. Marco Rubio of Florida, each of whom would have a hard time pressing forward without winning his home state.

Barring a massive upset, Trump appears poised to win Florida and sweep up its 99 delegates. In the RealClearPolitics average of recent polls, Trump held a massive 19-point lead over Rubio.

A Florida win would put Trump at 559 delegates, almost half the number of delegates needed to secure the Republican nomination. Though many delegates still need to be allocated, Trump would be far closer to the majority threshold than any of his rivals.

"Florida is do-or-die for the Rubio campaign, but it looks like victory may have slipped from his grasp," Patrick Murray, the Monmouth University polling director, said Monday in a statement accompanying a poll that found Trump with a comfortable 17-point lead over Rubio.

Trump's battle in Ohio against Kasich is much closer, according to the polls. And a victory by the frontrunner there would be a knockout blow to Kasich, who has said he will drop out if he does not win in Ohio.

After largely ignoring Kasich for months, Trump has turned up the heat on Kasich. Trump has blasted Kasich at almost every recent campaign rally and in daily tweets, hitting him for supporting free-trade agreements, for campaigning out of state, and for his overall strength as a leader.

"Kasich is a baby," Trump said Saturday during an Ohio rally. "He can't be president."

Trump tweeted multiple barbs at Kasich on Monday and Tuesday:

Trump's rivals are campaigning hard to deny him the winner-take-all primary states, even if that means ceding delegates to other candidates. Rubio suggested that his supporters should vote for Kasich in Ohio to stop Trump from getting the state's 66 delegates.

In particular, Trump's three opponents have all passionately criticized him since Friday for allowing violence to fester at his rallies. Trump canceled a high-profile Friday-night rally in Chicago as fistfights broke out at the event.

"Donald Trump has created a toxic environment," Kasich said Saturday.

Kasich continued:

And a toxic environment has allowed his supporters and those who sometimes seek confrontation to come together in violence. There is no place for this. There is no place for a national leader to prey on the fears of people who live in our great country.

John Kasich. REUTERS/Aaron Josefczyk

Though the media has focused mostly on Ohio and Florida, more delegates are up for grabs in the other states voting Tuesday. These three contests — North Carolina, Illinois, and Missouri — could send even more delegates Trump's way, or allow Cruz to stay in a competitive second-place position behind Trump.

Cruz has defeated Trump in multiple recent contests, including Kansas, Maine, and Oklahoma. And he has regularly outperformed his poll numbers.

The Texas senator could be looking at performing well in Illinois and Missouri in particular, two states in which he has staged numerous recent campaign events. Cruz's support in Illinois jumped in recent polls there. And the one reputable poll of Missouri's Republican voters found Cruz trailing Trump by just 7 points.

At a Monday press conference in Rockford, Illinois, Cruz sought to paint the GOP primary as a one-on-one race between him and Trump.

"This is now effectively a two-person race between me and Donald Trump," he said. "Only two candidates have any plausible path to winning the Republican nomination: me and Donald Trump."

Cruz went on to blast Trump for his ties to the "corruption" of Chicago Democrats: