Republican front-runner Donald Trump spoke in Palm Beach, Fla., after primary voters took to the polls in five states: Florida, Illinois, Ohio, Missouri and North Carolina. (Reuters)

THE MORNING PLUM:

With Donald Trump steamrolling towards the GOP nomination, the political chatter is increasingly focused on whether Trump could win a general election by making surprise inroads into states in the industrial Midwest. Many Democrats and nonpartisan observers see this as probably the only plausible (if that’s even the right word for it) path for Trump, who might do this mainly by running up huge numbers among white voters — particularly blue collar whites.

But a new examination of the demographics and projected voting patterns in some of the key Rust Belt states underscores just how unlikely this really is. To succeed, this analysis finds, Trump would likely have to improve on Mitt Romney’s advantage over Barack Obama among blue collar whites by double digit margins, which is an astronomically high bar — in almost all of these states.

Demographer Ruy Teixeira conducted this analysis at my request. Teixeira was the lead analyst on a comprehensive report on the projected makeup of the 2016 electorate that was released by the Center for American Progress late last year. He built on that report in this new analysis.

The rub of the matter is that Trump’s goal of winning by running up big margins among whites could be made even harder by ongoing demographic shifts that are slowly rendering even whiter Rust Belt states less white. The CAP report found that in a number of these states — Michigan, Wisconsin, Pennsylvania, and Ohio — the blue collar white share of the vote is projected to decline by at least two percentage points, and the overall white share is projected to drop by around one point.

I asked Teixeira to factor in these expected shifts to calculate how much better Trump would have to fare among working class whites than Romney did in order to win each state. In each of these, Teixeira assumes that the Democratic candidate (likely Hillary Clinton) will win the same share of the nonwhite and college educated white vote that Obama did, which, if anything, is generous to Trump. Given the overall margins that Obama won these states by — which are in some cases quite large — Trump would have to improve enormously on Romney’s performance among blue collar whites:

— In Michigan, where Romney beat Obama by 53-45 among working class whites, Trump would have to win among them by 62-36, an improvement of 18 points.

— In Wisconsin, where Romney beat Obama by 50-48 among working class whites, Trump would have to win among them by 56-42, an improvement of 12 points.

— In Pennsylvania, where Romney beat Obama by 56-42 among working class whites, Trump would have to win among them by 63-36, an improvement of 13 points.

— In Ohio, where Romney beat Obama by 57-41 among working class whites, Trump would have to win among them by 60-38, an improvement of six points. (This is lower than the others because Ohio was much closer overall; but even six points is a pretty sizable improvement.)

Now let’s be even more generous to Trump. Let’s assume he can win college educated white voters by larger margins than Romney did (which seems unlikely, though not impossible), and calculate how much he would need to improve over Romney’s performance among white voters overall, meaning among both working class and college educated whites taken as one group. (This again assumes the Dem wins among nonwhites by the same margins Obama did.) If you factor in demographic shifts, here’s what you get:

— In Michigan, where Romney beat Obama by 52-46 among white voters overall, Trump would have to win among them by 58-40, an improvement of 12 points.

— In Wisconsin, where Romney beat Obama by 50-49 among white voters overall, Trump would have to win among them by 54-45, an improvement over Romney of eight points.

— In Pennsylvania, where Romney beat Obama 54-44 among white voters overall, Trump would have to win among them by 58-40, an improvement of eight points.

— In Ohio, where Romney beat Obama by 56-42 among white voters overall, Trump would have to win among them by 58-40, an improvement of four points. (This seems doable, but again, this presumes Trump makes inroads among college educated whites and that the nonwhite spread remains the same.)

“It seems very unlikely that Trump can do so much better than Romney among whites and particularly working class whites in these states,” Teixeira tells me. “The swings are just too big.”

Now, Trump backers might argue that he will also drive up turnout among white voters relative to nonwhites, meaning he would not have to win among them by these margins to prevail. But here is where a demographic trap intrudes: All of the things that Trump might say and do to drive up white turnout — particularly working class white turnout — would also likely drive up nonwhite turnout. So there’s no reason to expect a major boost in turnout from one group and not the other, Teixeira says.

“I don’t think he can produce a tsunami of white turnout in these states without provoking an answering surge in minority turnout,” says Teixeira, who has a lot more comprehensive demographic analysis at his Election Oracle page. “The fact of the matter is that his path in the Midwest/Rustbelt is very, very difficult no matter how you look at it.”

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 * TEAM HILLARY PREPARES STRATEGY AGAINST TRUMP: The Post pulls back the curtain on the preparations underway by the Clinton campaign and Democratic groups for a general election against Trump:

They are now focused intently on researching the billionaire real estate mogul’s business record, dissecting his economic policies and compiling a long history of controversial pronouncements that have captivated and repelled the nation in this tumultuous election season….Because of the litany of controversial pronouncements he has made, they expect a Trump nomination to make it easier to rally women, Latino and African American voters to turn out for Clinton.

The story also reports that Democrats are working to understand the source of Trump’s economic message (such as it is) and its appeal to blue collar whites, which should not be neglected.

 * RNC CHAIR HINTS AT CONTESTED CONVENTION: On CNN’s State of the Union, RNC chair Reince Priebus was asked whether Trump should get the nomination if he emerges with a plurality, but not a majority, of delegates. his reply:

“When someone’s a little bit short, you let the process play out….the minority of delegates doesn’t rule for the majority. So this is a delegate-driven process….delegates matter. And so the majority of voting delegates in our party choose the nominee.”

Contested convention, here we come! Of course, Trump could win a majority of the delegates outright through primary voting, making the best laid plans moot.

* McCONNELL RULES OUT LAME DUCK CONFIRMATION: On Fox News Sunday, GOP Senate leader Mitch McConnell declared that Republicans will not vote on Merrick Garland, even in a lame duck session after a Democrat were elected president:

“The principle is the same. Whether it’s before the election or after the election, the principle is the American people are choosing their next president and their next president should pick this Supreme Court nominee.”

Never mind that Obama was elected twice by popular majorities. Okay, then — it looks like Republicans are now willing to court the risk of having another Dem president nominate someone more liberal than Garland.

* TRUMP VOWS TO DETAIL COURT PICKS: At a rally yesterday, Donald Trump promised to detail a list of people he’d nominate to the High Court as president:

“I’m going to get between five and 10 judges that everybody respects, likes and totally admires,” he said, adding that he would “guarantee it personally, like we do in the world of business, which we don’t like to do too often, but I will guarantee it that those are going to be the first judges that I put up for nomination if I win.”

His spokesman promises a list this week. This should be interesting, since after all, the GOP position is that President Trump should get to pick the next nominee (if elected), and the current president shouldn’t.

* WHY REPUBLICANS CAN’T ALLOW HEARINGS: E.J. Dionne explains why Republicans are not holding any confirmation hearings for Garland:

The central irony here: The very conservatives who use “judicial activism” as a battering ram against liberals are now the aggressive judicial activists. It’s precisely because Garland’s record reveals him to be a devout practitioner of judicial restraint that an intellectually frank dialogue over his nomination would be so dangerous to the right. It would expose the radicalism of their jurisprudence.

Republicans themselves have revealed they are not holding hearings explicitly because so doing would expose Obama’s nominee to the public and make it harder for them to oppose him.

* AMERICANS AGREE WITH OBAMA ON CUBA: With the President visiting Cuba for the early part of this week, a new CBS News/New York Times poll finds: that 58 percent of Americans favor re-establishing diplomatic relations, and 55 percent support ending the U.S. trade embargo. Even Republicans narrowly favor both of these things by 44-42 and 43-38.

Interestingly, however, a majority of Republicans disapproves of how Obama is handling relations with Cuba by 55-23 (when the question wording includes Obama’s name).

 * TRUMP SPENDS LITTLE TO WIN BIG: Politico looks at the latest campaign finance reports and finds that Trump has spent far, far less than all his rivals, even as he has good shot at winning the nomination. That’s remarkable. However:

It also worries Republicans who are not convinced that Trump’s barebones operation will fare well in a general election against a Clinton juggernaut that has spent nearly a year assiduously cultivating a major donor network, stockpiling cash and strategically building infrastructure across the country….Trump continues to mostly self-fund his campaign…he’s in no rush to tinker with a formula that has been paying huge dividends for him in the GOP primary.

This is not very good for Republican campaign professionals.

* AND COULD A TRUMP DEBACLE FORCE A GOP RETHINK? Paul Krugman suggests that if the GOP nominates Trump and an electoral disaster ensues, it could prompt Republicans to rethink whether they’ve been selling GOP voters a bill of economic goods:

Had Mr. Rubio succeeded, he would simply have encouraged his party to believe that all it needs is a cosmetic makeover — a fresher, younger face to sell the same old defunct orthodoxy….What we’re getting instead is at least the possibility of a cleansing shock — of a period in the political wilderness that will finally force the Republican establishment to rethink its premises. That’s a good thing — or it would be, if it didn’t also come with the risk of President Trump.

Of course, some will say that Trump was a big government liberal who couldn’t draw a sharp contrast with the Dem and that this proves the need to run a Real Conservative next time.