A recent CNN/ORC poll found that while Trump and Clinton perform extremely well against candidates of their own parties, they don't when competing across the aisle.
Bernie Sanders and Clinton both would beat Trump by double digits, according to hypothetical general election matchups.
Eliminate Trump, though, and Clinton's race gets a lot tighter. Ted Cruz would tie with her in a hypothetical matchup, and John Kasich would beat her by 6 points.
Kasich fares the best against the Democratic front-runner, yet only 17 percent of Republican voters polled want him to get the nomination.
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Presidential power rankings, 3/15
Trump, Clinton might not be best candidates to win general election
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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However, a large majority –– 65 percent –– of Republicans said if Trump wins the nomination, they would not want to see another Republican candidate run in the general election as a third-party candidate.
On the Democratic side, Sanders actually performs better than Clinton against every Republican candidate. But it's becoming more and more unlikely he'll get the Democratic nomination.