Many pundits once said Donald Trump never had a chance. But despite the Republican frontrunner's politically incorrect comments on Mexicans, Muslims and his closest rivals, his popularity is soaring. (Reuters)

THE MORNING PLUM:

If Republicans are going to have any hope of stopping the runaway train otherwise known as Donald Trump, it may rest on their ability to limit the breadth of his appeal. A single alternative to Trump — most likely Marco Rubio — could conceivably coalesce enough support among well educated, relatively affluent, more moderate Republicans or more mainstream conservatives and go on to triumph in winner-take-all March 15th states like Ohio and Florida, forcing a delegate showdown at the convention for the nomination.

Super Tuesday looms as a big test of this proposition. As Ron Brownstein puts it:

If Trump can beat Cruz…in heavily blue-collar and evangelical states on one side, and top Kasich and Rubio in white collar, less culturally conservative states on the other, it will grow increasingly daunting for any candidate to coalesce a coalition large enough to stop the front-runner.

The new CNN national poll casts further doubt on the likelihood of this working. It finds that Trump has expanded his lead among registered Republican and GOP-leaning independent voters nationally: He has 49 percent; Rubio has 16 percent; Cruz has 15 percent; Ben Carson has 10 percent; and John Kasich has nine percent. Two of the four days of polling were taken after last week’s GOP debate, which was supposed to be a dramatic game-changer for Rubio.

Donald Trump hinted on Feb. 28 that he might run as an independent, because the GOP is treating him "unfairly." It's not the first time he's made that threat. (Peter Stevenson/The Washington Post)

But perhaps Republicans should be even more alarmed about these findings, from the CNN poll’s internals:

— Trump is dominating among Republicans and GOP leaners who are college graduates, with 46 percent, to 19 percent for Rubio, 13 percent for Cruz, and nine percent for Kasich.

— Trump is dominating among suburban Republicans, with 51 percent, to 16 percent for Rubio, 13 percent for Cruz, and six percent for Kasich. As James Hohmann has reported, Rubio’s strategy is heavily focused on winning suburban areas in many Super Tuesday states and beyond.

— Trump is dominating among Republicans who make $50,000 or more, with 50 percent, to 16 percent for Rubio, 15 percent for Cruz, and eight percent for Kasich.

— Trump is dominating among Republicans who are under 55, with 47 percent, to 17 percent for Rubio, 14 percent for Cruz, and five percent for Kasich. (Unfortunately, the samples are too small to break out younger groups.)

These are very crude categories, to be sure. And it’s hard to know how much national numbers such as these tell us about upcoming state contests. But these findings raise at least the possibility that Trump’s appeal is proving much broader among Republican voters than expected. They also suggest the possibility that Rubio may not be able to beat Trump among more mainstream and more educated voters in the manner he must, in order to have any hope of catching Trump in the delegate count after a big Trumpian triumph on Super Tuesday.

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 * HILLARY DOMINANT AS SUPER TUESDAY LOOMS: The new CNN national poll also finds that Hillary Clinton leads Bernie Sanders among Democrats and Dem-leaning independents by 55-38. Note this:

Men, younger voters, independents and liberals are all about evenly split between Clinton and Sanders, while Clinton’s lead rests on large advantages among women, older voters, Democrats and moderates.

If Clinton is now splitting younger voters with Sanders, that might mean she is improving among a demographic that had been elusive for her and could matter in the general.

* TRUMP DOMINATING IN SOUTHERN STATES: NBC polls released over the weekend find Donald Trump leading Ted Cruz and Marco Rubio in Georgia (30-23-23) and Tennessee (40-22-19). NBC re-contacted close to 30 percent of respondents after last week’s GOP debate, which was supposed to be a huge breakout for Rubio, and found:

Movement in the GOP horserace was negligible, according to the re-contact interviews: Trump, Rubio and Cruz kept about 90 percent of their supporters; Carson kept about 80 percent of his; but Kasich kept only about 60 percent of his backers.

Meanwhile, new CBS News polls find Trump leading Cruz and Rubio in Georgia by 40-29-22 and Trump leading Rubio and Cruz in Virginia by 40-27-22. Rubio is making a big play for Virginia, too.

* BUT TED CRUZ LEADS IN TEXAS: The new NBC polling finds Cruz leading Trump and Rubio in Texas by 39-26-16. And the new CBS polling puts it at 42-31-19. Interestingly, it would be in Rubio’s interest for Trump to beat Cruz in Texas, to make it harder for Cruz to remain in the race.

But that doesn’t look likely at this point, meaning Cruz may stay in past Super Tuesday, making it harder for Rubio to consolidate the non-Trump vote, heading into the crucial March 15th winner-take-all contests.

* RUBIO’S NEW STRATEGY: JOINING ‘THE CIRCUS': The New York Times takes stock of the new, feisty, insult-spewing Marco Rubio, and offers this fascinating explanation for his change in approach:

“We came to the conclusion that if being a part of the circus is the price you have to pay in order for us to ultimately be able to talk about substantive policy, then that’s what we’re going to do,” said Todd Harris, a senior Rubio adviser. Mr. Harris noted that Mr. Rubio’s speeches were now being carried live on television. And if the price of admission, he added, was talking about “how Trump is a con man, with a bad spray tan,” so be it.

Well, if Rubio gets blown out on Super Tuesday, getting his speeches carried live on TV will have provided a consolation prize of sorts.

* GOP WILL PROBABLY UNITE BEHIND TRUMP: The Post has a good piece on the handwringing and panic among Republicans as they contemplate the possibility that a Trump nomination could split their party. Note this:

Richard Wadhams, a former chairman of the Colorado Republican Party, said there has been a growing acceptance of Trump in recent weeks among party leaders and rank-and-file activists alike. “There’s a strong possibility that Trump is going to be the nominee, and a lot of Republicans are ready to accept that even though they’ve not been supporters of him,” Wadhams said. “The penchant to defeat Hillary Clinton will transcend any concerns about the way Trump has conducted himself.”

Of course. Republicans can just say that Trump is the lesser of two evils as their excuse for uniting behind him, and the #NeverTrump hashtag will disappear down the memory hole.

* HILLARY CRUSHING IT IN SOUTHERN STATES: The new NBC News polls find Hillary Clinton with enormous leads over Bernie Sanders in Georgia (64-30), Tennessee (60-34), and Texas (59-38). The new CBS News polls have Clinton leading in Georgia by 65-35, leading in Virginia by 59-39, and leading in Texas by 61-37.

* BERNIE FACES STEEP UPHILL CLIMB: After Hillary Cinton’s blowout win in South Carolina, Nate Cohn explains what to look for on Super Tuesday, which will be fought in a lot of states with heavily African American populations:

The likelihood of a Clinton landslide in the delegate-rich South means that Mr. Sanders can’t compensate with a few narrow, feel-good wins outside the South. The thing to watch on Tuesday night is whether Mr. Sanders can win by big — even double-digit — margins in states like Minnesota or Massachusetts. The margins matter, because delegates are awarded proportionally in the Democratic nomination contest.

And as Cohn notes, the races are pretty tight in the non-southern Super Tuesday states, so Sanders may not be able to run up delegate totals to offset her expected dominance elsewhere.