Sources both inside and close to the White House are worrying about a loss of energy among the President's base — or as one advisor colorfully put it, the folks who'd "walk over glass" for Trump.

Two trends that are troubling them:

Trump's strong approval has fallen quickly: As Nate Silver outlines in this late May article titled "Donald Trump's base is shrinking": "There's been a considerable decline in the number of Americans who strongly approve of Trump, from a peak of around 30 percent in February to just 21 or 22 percent of the electorate now. (The decline in Trump's strong approval ratings is larger than the overall decline in his approval ratings, in fact.) Far from having unconditional love from his base, Trump has already lost almost a third of his strong support." Slide among whites without college degrees: Only 46% of whites with no college degree approve of the way Trump is handling his job as president, according to the most recent Quinnipiac University poll. In the same poll in early March, 60 percent of whites without college degrees — a group that was key to Trump's victory — approved of his job performance.

Caveats: These are national, not state numbers, and it's normal for a President's numbers to creep down from the start of the presidency. The numbers are also volatile: If Trump delivers some big policy wins, he could quickly reverse these trends.

But the concerns are real: Some White House advisors are worried that if these most intense supporters lose their passion for him, there'll be no way to regain the energy in time to fight off a fired-up left in 2018.

Some White House advisors are worried that if these most intense supporters lose their passion for him, there'll be no way to regain the energy in time to fight off a fired-up left in 2018. An evolving line of thinking: Trump will probably never be at 51% approval — the "strongly disapprove" number against him, which is around half the voting public, makes that virtually impossible. The strategy, therefore, has to involve keeping the diehard ginned up and driving up Trump's "strongly approve" numbers. There's little hope of converting Democrats — beyond the Midwest working class who already voted for Trump. So it's crucial to keep a large enough base that's willing to walk over glass for the President.

Trump will probably never be at 51% approval — the "strongly disapprove" number against him, which is around half the voting public, makes that virtually impossible. The strategy, therefore, has to involve keeping the diehard ginned up and driving up Trump's "strongly approve" numbers. There's little hope of converting Democrats — beyond the Midwest working class who already voted for Trump. So it's crucial to keep a large enough base that's willing to walk over glass for the President. The Paris model: A good number in the administration recognize Trump's withdrawal from the Paris deal as an example of him delivering for his base. Their view: It's irrelevant that most Americans don't support withdrawing from Paris because there's not one person who supports the climate deal — and who actually votes on it — that would ever be persuaded to vote for Trump.

A good number in the administration recognize Trump's withdrawal from the Paris deal as an example of him delivering for his base. Their view: It's irrelevant that most Americans don't support withdrawing from Paris because there's not one person who supports the climate deal — and who actually votes on it — that would ever be persuaded to vote for Trump. As Silver puts it: "voters who strongly disapprove of Trump outnumber those who strongly approve of him by about a 2-to-1 ratio, which could presage an 'enthusiasm gap' that works against Trump at the midterms."

Trump still reads the polls intensely, even though he no longer boasts about them publicly. Advisors say he knows he's screwed if he can't deliver on the big promises like repealing Obamacare, cutting taxes and building the wall. He seemed to indicate that last week, when he kicked off a closed-door meeting with congressional leaders by saying that the base was strong and it was time to come through for them.