THE MORNING PLUM:

Only 12 hours after Donald Trump effectively sealed the GOP nomination with his big Indiana win, the presumptive GOP nominee immediately reminded Republicans that the nightmare otherwise known as Trumpism — from which they had hoped to awaken — is now all too real.

On Morning Joe today, Trump doubled down on one of his most controversial positions: His call for a ban on non-citizen Muslims from entering the United States. Asked whether he will stand by his Muslim ban as the GOP nominee, Trump said:

“We have to be very vigilant. We have to find out what’s going on….We have a president that won’t mention the term ‘radical Islam’….We have to be vigilant. Yes. We have to find out what the hell is going on. There’s no doubt about it.”

So, yes, the Muslim ban stands. Meanwhile, on the Today Show, Trump vowed to unify the GOP, but in the next breath, basically told Republican critics who don’t like him to get lost:

In a shot at his critics, Trump added: “Those people can go away and maybe come back in eight years after we served two terms. Honestly, there are some people I really don’t want.”

And a new CNN poll out this morning underscores how deeply flawed a nominee he is likely to prove. The poll shows Hillary Clinton leading Trump nationally by 54-41.

But more important, the new CNN poll finds Trump is viewed unfavorably by 64 percent of women; 73 percent of nonwhites; 70 percent of voters under 35;  67 percent of college graduates; and 57 percent of moderates. Those are mostly constituencies the GOP had hoped to improve among. And while it’s often rightly pointed out that Clinton is disliked, she fares substantially better than he does among most of those particular groups, who will be pivotal to Clinton’s hopes of reconstituting the Obama coalition this fall.

And on top of all this, the CNN poll shows that Trump is also viewed unfavorably by 37 percent of conservatives, suggesting the possibility that some might potentially support a third party challenger, or if no such challenge materializes, at least stay home.

After losing the Republican primary in Indiana, Sen. Ted Cruz (R-Tex.) said he was "leaving it all on the field." GOP front-runner Donald Trump commended Cruz, calling him "a tough, smart competitor" - a complete reversal from the insults he had been using earlier in the day. (Sarah Parnass/The Washington Post)

Obviously those numbers could change over time. But Trump — who is plainly susceptible to allowing the giddy highs of victory to cloud his capacity to reason — is not showing any awareness that the general election audience might see his antics differently than GOP primary voters do. And if Trump’s numbers among key voter groups, including conservatives, continue to tank — which could very well happen, once Democrats get serious about unleashing a sustained national attack on him — that could pose a stark choice for GOP officials and Republican lawmakers up for reelection amid a presidential year electorate, in states carried by Obama. As Jonathan Bernstein explains:

It’s hard to imagine a bigger disaster for the Republican Party. It is left with a likely nominee who appears to be an awful — historically awful — general-election candidate and who is also the least committed to the Republican agenda in decades.

This leaves a terrible choice for GOP politicians and other party actors. Support Trump, and they’ll always be associated with him and they’ll be tarred with whatever irresponsible things he says. Oppose him, and he’ll be an even weaker general-election candidate who could bring down the entire Republican ticket in November, costing them not only the closely contested Senate but perhaps even the House and several state legislative chambers.

One last point: If Republican lawmakers and officials do distance themselves from Trump in meaningful numbers, that could really end up mattering. As Democratic strategist Simon Rosenberg argues, Democrats are likely to be far more unified, creating a vivid contrast:

It will also be remarkable to see a very popular set of Democratic leaders – Biden, Bill Clinton, both Obamas, Sanders, the Vice President – standing alongside and campaigning with Secretary Clinton in the months ahead. That image of a powerful team lead by an experienced leader (and first woman!) will not be easily answered by an unpopular, isolated Trump and a deeply unpopular party….An unprecedented “Democratic Team” that includes two former Presidents could end up being an extraordinary advantage for her this fall.

Nice job, GOP voters.

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* TRUMP IS A DEEPLY FLAWED CANDIDATE: Nate Cohn explains just how flawed Trump is as a general election candidate. He trails Hillary Clinton by large margins in national polling, and there’s also this:

He even trails in some polls of several states where Mitt Romney won in 2012, like North Carolina, Arizona, Missouri and Utah…. Mr. Trump…would be the most unpopular major party nominee in the modern era, with nearly two-thirds saying they have an unfavorable opinion of him….Mr. Trump’s ratings are worst with the voters who made up the so-called Obama coalition of young, nonwhite and well-educated voters who propelled President Obama’s re-election four years ago.

As I’ve noted, Trump is even marginally under water with blue collar whites and white men, making his scheme to ride working class white anger into the White House more far fetched.

* WHY GOP VOTERS PICKED TRUMP: Nate Silver offers some persuasive reasons:

Republican voters were swayed by Trump’s arguments that the candidate with the most votes and delegates should be the nominee….Some voters might have prefered Cruz or John Kasich…but not at the expense of a contested convention in which the plurality winner would be denied the nomination. Trump’s main differentiator was to double-down on cultural grievance: grievances against immigrants, against Muslims, against political correctness, against the media, and sometimes against blacks and women. And the strategy worked.

Trump won in part because a lot of GOP voters agree that the GOP establishment is rigging the system against him (and them), and agree with his calls for mass deportations and banning Muslims.

* SOME REPUBLICANS STICK WITH ‘NEVER TRUMP’ VOW: The New York Times has a good roundup of all the GOP lawmakers, strategists, and media figures who are now renewing their vow never to support Trump as the nominee. But:

Mr. Trump…asserted, without offering any names, that many of those who had mocked him in the past were now privately pledging their support. “They are calling now,” he said, with characteristic bravado. “And they are calling to say, ‘We’d love to get on the train.’ The Trump train. We have a lot of people coming.”

Well, if Trump has a whole lot of secret GOP endorsements coming, that changes everything.

* TRUMP FACES BIG DECISION ON SUPER PACs: On Morning Joe today, Trump was asked whether he would “welcome the support of Super PACs in the general election.” He replied:

“I’m going to be making a decision over the next week. I do love self funding…but we do need money for the party. The party will come together….Do I want to sell a couple of buildings and self-fund? I don’t know that I want to do that, necessarily. But I really won’t be asking for money for myself. I’ll be asking for money for the party.”

That sounds like he’s already rehearsing his justification for embracing Super PAC spending on his behalf, which could undercut one of his key arguments against Clinton as a creature of the establishment.

* BERNIE WINS INDIANA, BUT MATH REMAINS UNCHANGED: Bernie Sanders beat Hillary Clinton by 53-48 in Indiana yesterday, but he only netted six delegates: He picked up 43, while Clinton earned 37. As the Associated Press puts it:

Sanders’ win in Indiana likely won’t make much of a dent in Clinton’s lead of more than 300 pledged delegates. Clinton is still more than 90 percent of the way to clinching the Democratic nomination when the count includes superdelegates.

Meanwhile, senior Sanders adviser Tad Devine has acknowledged to me that Sanders will need big gains in closing the pledged delegate gap to have any prayer of winning superdelegates.

* SANDERS IS HANGING IN THERE: The Vermont Senator says in an interview on CNN that he’ll keep fighting until the end:

“I think that it is basically irresponsible and extremely undemocratic to say to the people of West Virginia, Kentucky, Oregon, California — our largest state — that they should not have the right to cast a ballot to determine who the president of the United States will be, or what the agenda of the Democratic Party will be. I think that’s pretty crazy stuff.”

It’s fine for Sanders to fight until all the votes are counted. It’s another thing entirely for him to keep on trying to flip super-delegates after losing in the pledged delegate and popular vote count, though.

* HILLARY LOOKS TOWARDS NOVEMBER: Despite Sanders’s Indiana win, USA Today reports that the Clinton campaign is turning towards the general election, with campaign manager John Podesta releasing this statement:

“Throughout this campaign, Donald Trump has demonstrated that he’s too divisive and lacks the temperament to lead our nation and the free world….While Donald Trump seeks to bully and divide Americans, Hillary Clinton will unite us to create an economy that works for everyone.”

The contrast between Clinton (who, whatever her flaws, is seen as having commander in chief qualities) and Trump on temperament will loom large.