Standing in the rain outside the White House on Friday morning, press secretary Sarah Sanders talked with Fox News about President Trump’s push for a wall on the border with Mexico.

Asked by a “Fox & Friends” host whether the Senate should end the filibuster in order to pass legislation with a flat majority that would approve $5 billion to fund the wall, Sanders said it should.

“This is such an important issue, and it’s something that all of America wants to see happen,” Sanders said. “And, frankly, Americans want to be protected. . . . We can’t be a sovereign country if we don’t have borders and we don’t have protection of American citizens.”

Standard rhetoric except for Sanders’s telling assertion that “all of America wants to see happen.”

That’s simply not true. A Quinnipiac University poll released this week found that more than half of Americans oppose building a wall. That opposition has narrowed over the course of Trump’s presidency, but we’re far from a point at which most (much less “all”) Americans back the proposal.

As for the debate of the moment, we noted last week that 25 percent of Americans think building a wall on the border is an immediate government priority. Most Americans, including more than a quarter of Republicans, don’t think the government should be shut down to try to force funding for a wall — the direction in which we seem to be headed.

The views of Republicans here are important. In Quinnipiac's poll, 86 percent of Trump's party backed the idea — slightly more than view Trump's presidency favorably. The best approximation of what “all of America” might mean in this case is “all of the Republican Party,” a phrase that Trump seems to conflate with America at large with some regularity.

Sanders may just be using hyperbole for effect. Trump often seems to believe that his efforts have more support than they do — even beyond his frequent claims that polling understates his support. His base is his primary focus, and at times he seems baffled that it shouldn’t be.

Part of this, certainly, is that Trump joins many of his supporters in an isolated media environment. Fox News, which Trump watches regularly, has mentioned the wall far more in its coverage over the past year than has MSNBC or CNN. Fox Business, another Trump favorite, has mentioned it even more. According to closed-captioning data from the Internet Archive, Fox News mentioned the wall in about 1 out of every 12 15-second segments it aired on Thursday.

Fox News’s coverage has been credited with swaying Trump on the issue. He seemed to be prepared to accept that wall funding was a non-starter, prompting furious coverage on Fox News. In March, his apparent decision to approve a funding bill shifted after he saw critical coverage on Fox News; it seems that the same thing may have happened this week.

Trump follows only 45 people on Twitter. That’s down one from earlier this week. After conservative Ann Coulter criticized him harshly over the wall, Trump unfollowed her. It was a remarkable response that indicates how unused to criticism he is from within his protective circle. Even within his narrow media universe, things can be pulled tighter.

One of the underrecognized aspects of Trump’s presidency is how extensive his isolation is. He has held a slew of campaign rallies because he gets to interact with people who love him. His time off is at Trump Organization properties where people literally pay for the privilege of getting access. His administration, as The Washington Post’s Aaron Blake notes, is increasingly made up of people who will tell him what he wants to hear, particularly once Defense Secretary Jim Mattis heads for the exit.

The net effect of this is that Trump’s world is whipped into a frenzy over the necessity of the wall, and he hears little argument to the contrary. That frenzy, to some extent, derives from his supporters in the media and the White House believing that his success is entirely dependent on keeping his base close and believing that the wall is essential to accomplish that goal.

Again, Trump’s not entirely alone in this isolation. Among those who support Trump the most fervently, Fox News is by far the most trusted media outlet, according to a recent Post poll. More than half of Republicans routinely pick Fox as their most trusted news or opinion outlet in Suffolk University polling, too.

The result? As Cook Political Report’s Amy Walter noted on Twitter on Thursday, Republicans can see even bad news through a lens that’s favorable to the president. She pointed to an NBC-Wall Street Journal poll that was similar to ones taken after wave elections in 2006 and 2010.

When Democrats retook the House in 2006, 47 percent of Republicans said it sent a message to President George W. Bush that he needed to change his policies, while 17 percent said no message was sent. In 2010, 52 percent of Democrats said that the blowout sent a similar message to President Barack Obama.

This year? Only 22 percent of Republicans said the big swing in the House sent a message to Trump. Nearly half said it didn’t. A YouGov poll (conducted before many of the House results were finalized, to be fair) reinforced that idea: Forty-six percent of Republicans said their party won the midterms, while another 29 percent figured it was a wash.

If everyone around you is cheering and everyone you see on television is cheering, why would you think that anyone wasn't? It's a variant on what we might call Trump Rally Syndrome: The tendency of extrapolating outward from a small group of boisterous supporters to the public on the whole.

Consider this tweet from the Financial Times' U.S. managing editor.

That GoFundMe for building the wall is now at $11.6 million raised, a sizable sum. (Though only about 0.06 percent of the estimated cost of the wall.) Does this send a message to Trump that his wall — and his presidency — are popular?

Those donations average about $61 per donor as of writing. A bit fewer than 200,000 people have given — a small fraction of the country. It’s even a small fraction of the number of Americans who support building the wall.

The wall isn’t very popular. But, then, neither is Trump, and, thanks to the world in which he operates, that doesn’t seem to have dissuaded him much, either.