President Trump’s job approval rating cratered to its lowest point since he took office, with just 35 percent of Americans approving of his performance — and that was before his angry defense of a white supremacists rally, a new poll said Wednesday.

Roughly 55 percent of those surveyed do not approve of the job the president is doing, the Marist College poll said.

Although he remains popular with Republicans, with 79 percent approving, that number is down from his 91 percent approval rating among GOP respondents in June.

“While Republicans are still largely in Trump’s corner, the cautionary tale for the president lies in the softening of support at his base,” said professor Lee Miringoff, director of the Marist College Institute for Public Opinion.

“Since his numbers among Democrats and independents are weak, a crack among his most ardent supporters is something Trump can ill afford.”

Professor Larry Sabato, director of the University of Virginia’s Center for Politics, said the numbers are an ominous sign for Team Trump.

“For many months I’ve said Trump’s hard floor was 35 percent — that is, even in bad times, he’s likely to retain a third of the country. Those are his base Republican and independent backers,” he said.

But Tuesday’s remarkable press conference, in which a defiant Trump once again blamed “both sides” for the weekend violence in Charlottesville, Virginia, could threaten that number.

“No question, yesterday’s press conference may test the strength of that floor,” he added.

Trump on Tuesday condemned the violent white supremacists and neo-Nazis at the “Unite the Right” rally — but also said there were a lot of good people among the torch-bearing crowd, many of whom chanted Nazi and anti-Semitic slogans and carried swastika flags.

And he hammered the anti-racist and anti-fascist counter-demonstrators, accusing them of being equally guilty of the violence and appearing to suggest a moral equivalence between the two sides, enraging both Republicans and Democrats.

The poll also showed that those who view the president unfavorably feel more strongly about it than those who still like him by more than 2 to 1.

Of those who disapprove, 42 percent feel strongly about it compared to 20 percent who strongly approve, signaling a further erosion of support.

At a similar time in President Barack Obama’s tenure, 55 percent of registered voters approved of the job he was doing while 35 percent disapproved, according to the Marist survey.

More Americans, 60 percent, had a negative impression of Trump, including 20 percent of Republicans, while 34 percent had a favorable view of him.

Another 60 percent do not believe he is honest and trustworthy, while 37 percent believe he is.

And 72 percent of Americans think the president’s tweetstorms are reckless and distracting while 20 percent say they are effective and informative.

Overall, nearly two in three respondents — 64 percent, up slightly from 60 percent in March — report they are embarrassed by Trump’s behavior. Twenty-nine percent say they are proud of him.

And when it comes to his boast that only he could “Make America Great Again,” only 36 percent of Americans think the president is winning that battle compared with 59 percent who characterize him as losing.

When it comes to foreign policy — as the US wrangles with North Korea, Iran and Russia — Americans believe the president has weakened the US position on the global stage by a nearly 2-to-1 margin, 62 to 33 percent.

This survey of 1,009 adults was conducted between Aug. 8 and Aug 12.

The margin of error for all of those polled was 3.3 points, while the margin for registered voters, the majority of those polled, was 3.1 points.