It could be a chance for Bernie Sanders to gain momentum against Hillary Clinton on the Democratic side, or for Clinton to again show her strength by piling up a near-insurmountable delegate lead.
Republican and Democratic voters in five states will head to the polls Tuesday night with a swath of delegates at stake in each race.
Trump is looking for the "knockout blow" -- wins in the winner-take-all states of Florida, which awards 99 delegates, and Ohio, which allocates 66 delegates. It would provide him with a very clear path to the 1,237 delegates needed to clinch the nomination.
On the Democratic side, Clinton is aiming to bounce back after a stunning loss to Sanders in Michigan. She remains the Democratic frontrunner and leads Sanders by more than 200 pledged delegates.
Our rankings are based on the Real Clear Politics averages of national polls and those in states voting Tuesday (with the exception of Missouri, which has not been polled in months). We also factored in the candidates' delegate counts and their relative paths to the nomination, as well as their momentum (or lack thereof) over the past few weeks.
Since our most recent ranking, one more Republican candidate has dropped out of the race: retired neurosurgeon Ben Carson.
Here's a look at where all the candidates stand.
All poll results as of Monday.
Presidential power rankings, 3/15
POWER RANKINGS: Here's who has the best chance at being our next president
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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To the polls! First, here's a look at each candidate's national polling average.