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.
Click through the 3/15 presidential power rankings:
Presidential power rankings, 3/15
The GOP's last, best chance to stop Donald Trump is here
6. Marco Rubio, Republican, senator from Florida
Rubio's fortunes have fallen by the wayside over the past two weeks, and he has fallen the most in our rankings.
He now faces a virtual must-win in his home state that he seems destined to lose.
Polls show Rubio down nearly 20 points to Trump in Florida, a state he once guaranteed he would win. If he doesn't pull off what would, at this point, be a historic comeback, he would face mounting pressure from Sen. Ted Cruz of Texas, and possibly Gov. John Kasich of Ohio, to exit the race.
National polling average among Republican voters: 18% (3rd)
Super Tuesday state average: 12.9% (4th)
Last month: 3
(Photo by Gerardo Mora/Getty Images)
5. John Kasich, Republican, Ohio governor
Kasich faces a similar challenge as Rubio: The primary in his home state of Ohio on Tuesday is do or die.
Unlike Rubio, he appears to have a shot at knocking off Trump in that state. Polls have shown him ahead of the mogul by about 4 points heading into the Buckeye State's primary as he tries to become the Republican establishment's latest (and perhaps final) weapon against Trump.
Those who talk up Kasich say he is a successful governor of a swing state with a record to point to, and clear bipartisan appeal. He also has a plethora of experience from nearly two decades in Congress, including foreign-policy areas and his time as chair of the US House budget committee.
But that same bipartisan brand has hurt Kasich with the GOP base. He is to the left of most GOP candidates on immigration reform, and he expanded the federal Medicaid program under the Affordable Care Act — two issues that could doom him with hard-line conservatives.
National polling average among Republican voters: 12% (4th)
March 15 state average: 19% (3rd)
Last month: 6
(Photo by Jeff Swensen/Getty Images)
4. Bernie Sanders, Democrat, senator from Vermont
Sanders not only upset Clinton in New Hampshire last month; he also achieved a gigantic, 22-point victory, a feat unthinkable to observers months ago.
He suffered a small setback in Nevada and a huge one in South Carolina, where he lost to the former secretary of state by nearly 50 points. Then he shocked again with an upset win in Michigan.
Nevertheless, it is becoming increasingly clear that Sanders' path to the nomination is tightening. He faces challenging delegate math ahead, needing to win about 54% of the remaining pledged delegates to overtake Clinton.
National polling average among Democratic voters: 39.6% (2nd)
March 15 state average: 38.3% (2nd)
Last month: 5
(Photo credit MICHAEL B. THOMAS/AFP/Getty Images)
3. Ted Cruz, Republican, senator from Texas
Cruz has mounted something of a comeback over the past two weeks, becoming clearly best positioned among the Republican field to take on Trump.
He won three contests on Super Tuesday, two more on March 5, and Idaho's contest last week. The map gets more challenging after Tuesday, with April dominated by Northeast and mid-Atlantic contests more favorable to Trump.
Still, Cruz inspires a flood of enthusiasm among the GOP base, and he may be the best-positioned candidate from within the political sphere to back up the notion that he's not a typical politician, that he is the outsider the base wants despite his day job in Washington.
And his eye-popping fund-raising numbers mean he could be in the race for the long haul — perhaps all the way to the convention.
National polling average among Republican voters: 21.8% (2nd)
March 15 state average: 23.2% (2nd)
Last month: 4
(Photo by Charles Ledford/Getty Images)
2. Donald Trump, Republican, businessman
Trump has lit the political world on fire since his entry into the race last summer, and he has showed surprising staying power. We're now on month No. 10 of "The Trump Show."
He has won 15 of the 25 decided contests, something unthinkable when he entered the race in June. And he appears closer than ever to finishing off his rivals: With wins in Florida and Ohio, he could amass more than 160 delegates and would see a clear path to the 1,237 majority needed to clinch the nomination.
There's a clear appetite among Republican primary voters for someone like Trump, who entered the race to controversy surrounding his position on illegal immigration. Business Insider discovered more of that when we followed him on the trail for a week.
National polling average among Republican voters: 36% (1st)
March 15 state average: 38% (1st)
Last month: 2
(Photo by Andrew Harrer/Bloomberg via Getty Images)
1. Hillary Clinton, Democrat, former secretary of state
She suffered a setback last week in Michigan but still ended that night with more pledged delegates than Sanders. The delegate math is on her side going forward.
The long-presumed Democratic nominee, Clinton has been a shakier-than-expected candidate. But she has a clear look at the nomination, and she would enter the general election with a slight advantage over the likely Republican nominee of Trump or Cruz.
National polling average among Democratic voters: 51% (1st) March 15 state average: 54.3% (1st)
Last month: 1
(Photo by Daniel Acker/Bloomberg via Getty Images)
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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.
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.
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.
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.
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: