Donald Trump won two important endorsements last week – endorsements he’ll very soon regret. Democratic Sen. Elizabeth Warren endorsed Trump’s tax plan, and the New York Times’ Paul Krugman praised Trump’s understanding of economics.

Trump is enjoying a populist surge right now, but it’s early in the primary process. People answering polls right now are interested in sending messages with their responses – they’ll worry about electability later.

When the primary race gets serious, as it will later in the fall, the words of Sen. Warren and Krugman will be back to haunt Trump.

“There are a lot of places where he gets out and talks about important things,” Sen. Warren said on a television talk show. “Donald Trump and I both agree that there ought to be more taxation of the billionaires, the people who are making their money on Wall Street.”

It wasn’t quite an endorsement for the presidency, but it’s enough. Voters – actual voters, not the “likely voters” who answer those summer polls – know that Sen. Warren is one of the most left-leaning lawmakers on Capitol Hill. They know her redistributionist policies would lead to an economic death-spiral.

Sen. Warren is so wrong about economics that even President Barack Obama has chided her understanding of it. “She’s absolutely wrong” about his trade policies, he said.

When you’re so far to the left that even Obama says you’re off the rails, that’s a sign that your endorsement might not help a Republican.

Likewise, Krugman’s blessing isn’t something a GOP presidential candidate ought to be proud of.

“Mr. Bush has chosen to attack Mr. Trump as a false conservative, a proposition that is supposedly demonstrated by his deviations from current Republican economic orthodoxy: his willingness to raise taxes on the rich, his positive words about universal health care,” Krugman writes. “And that tells you a lot about the dire state of the G.O.P. For the issues the Bush campaign is using to attack its unexpected nemesis are precisely the issues on which Mr. Trump happens to be right, and the Republican establishment has been proved utterly wrong.”

Like Sen. Warren, Paul Krugman has proven to be spectacularly wrong, time and time again. He fought hard for the 2009 stimulus package – and when it failed to bolster the economy, he claimed that was because it wasn’t big enough.

He claimed Germany’s austerity was a mistake and that Greece’s deficit spending would pull that country out of recession. Today, Germany is thriving and Greece is (again) on the verge of collapse.

The real point here is that for all of Trump’s heady popularity today, policies matter – and Trump’s policies are completely out of line with the Republican electorate.

Who gets up and goes to vote on Election Day? Who organizes get-out-the-vote efforts? Who works the phone banks? It’s the party’s base – the activists. They organize and they turn out to vote. These are the people Trump can’t hold onto.

Sure, he’s having a great time now. But soon, GOP voters will reject Trump and his flawed economic policies.