Opinion polls are flashing warning signs for President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE — and in some unexpected ways.

Recent national polls — most notably one from Fox News that incurred the president’s ire — have shown Trump slipping even among groups that have long been perceived as pillars of his support.

In the Fox News poll released last week, Trump was tested against four possible Democratic opponents: former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and Sens. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.), Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.).

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Trump won white voters by relatively narrow margins against all four — from just a single point over Biden to 7 points over Harris. That’s bad news for Trump, who enjoyed a 20-point advantage with white voters over Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE in 2016.

The president crushed Clinton with white non-college educated voters, winning them by a huge 37 points (66-29 percent) over Clinton. In the Fox poll, his best performance with such voters — an 18-point advantage over Warren — was roughly half as large.

The Fox News poll does not appear to be an outlier, as a Quinnipiac University poll released last month showed similar patterns.

Against the same four Democratic contenders, Trump’s biggest margin in that poll with non-college whites was again over Warren, at 19 points.

It’s early in the race and Trump does not have one Democratic candidate to run against, which could hinder his polling ratings in head-to-head matchups for the time being.

At the same time, the figures indicate an erosion among the citadels of his support in 2016. Democrats argue the data points show Trump has taken some hits with his political base, even as his overall approval ratings have remained relatively static.

“After seeing him in office and many of the negative projections about him having come true, he is definitely losing some of those voters,” said Democratic consultant Bill Carrick.

Part of the problem for Trump lies in “raising their expectation that he was going to do something dramatic about the economy in the old industrial base,” Carrick said. “That hasn’t happened. To the extent that the economy is working, it’s working for more upscale voters.”

Similar dynamics are at play with more tightly contested groups. According to the 2016 exit polls, Trump won suburban voters by 4 points over Clinton. In the Fox News poll, he lost suburban voters to all four of the leading Democratic contenders — by 4 points to Harris, 6 points to Warren and Sanders, and 9 points to Biden.

Given the fine needle that Trump threaded to get elected in the first place, this all looks like very bad news for his reelection hopes.

In 2016, Trump lost the popular vote to Clinton by about 2 percentage points but won the presidency in large part by carrying the key states of Pennsylvania, Wisconsin and Michigan by very narrow margins.

That leaves Trump with very little leeway in 2020.

“We saw in the midterms that there was movement toward Democrats in every segment of the electorate,” said Democratic pollster Mark Mellman, who is also a columnist for The Hill. “That included non-college educated whites, it included rural voters, it included small-town voters. All those groups have diminished their support.”

There are caveats, to be sure.

Republicans believe Trump’s standing will improve once he has a specific Democrat to run against. The eventual nominee will receive much more intense scrutiny than has been the case so far and will have tens of millions of dollars of negative advertising run against them.

A prolonged Democratic primary could also help Trump, especially if it turns bitter, while he faces no truly serious challenge for the GOP nomination.

And there is also the broader question of how to view polls so far out from a general election.

Republican pollster David Winston highlighted the fact that the president generally enjoys stronger approval ratings on his handling of the economy than on his job performance overall.

To Winston, this suggests that there is a sizable swathe of voters who “see the numbers going in the right direction” but are not fully in Trump’s camp.

“They are looking for it to translate to a personal level,” said Winston. “That is the challenge in front of him. If he can do that, that will put him into a much stronger position.”

But there are plenty of indicators that are gloomier for Trump.

In the Fox News poll, for example, his overall approval rating of 43 percent was higher than his numbers against the potential Democratic challengers, which hovered round 39 percent.

Kyle Kondik of the University of Virginia's Center for Politics said this trend, which has also been seen in other polls, “suggests that even some people who like his job performance remain very conflicted about actually supporting him.”

Kondik added: “Trump got elected in large part because he was able to do well among voters who disliked both him and Hillary Clinton — in other words, he was able to get people who didn’t like him to vote for him anyway. There are some signs right now that he may not even be getting the support of everyone who approves of him, a worrying sign for a president whose approval rating is consistently lower than his disapproval rating.”

Democrats are cautious, mindful of the huge shock of Trump’s victory in 2016. But, for now, they believe Trump's standing favors their nominee, whoever she or he may be.

“I was so wrong the last time that I’m scared of the prediction business” said Carrick. “But I would say that if I were in his camp and looking at this, I would not be very optimistic.”

The Memo is a reported column by Niall Stanage, primarily focused on Donald Trump’s presidency.