President Donald Trump warned Google, Facebook and Twitter “better be careful,” charging them with altering search results and other functions to push a liberal political agenda.

After nearly 48 hours of battle with the late Sen. John McCain, R-Ariz., even after his death, the president needed a new foe on Tuesday. Or at least a new way to change the subject and drive the day’s narrative.

“They better be careful because you can’t do that to people,” he warned the companies, claiming to have gotten “thousands and thousands” of complaints.

“I think that’s a very serious thing, and I think that’s a very serious charge,” he told reporters during an unrelated photo opportunity. “I think it’s a very serious charge.”

[Move to Rename Building for John McCain Stirs Southern, Party Debates]

He said the tech giants are “really treading on very, very troubled territory,” adding the alleged practice is “not fair to large portions of the population.”

That followed a pair of morning tweets in which he alleged Google’s search algorithms are intentionally designed to return “only the viewing/reporting of Fake New Media.” That means, in his view, the tech giant has its search function “RIGGED, for me & others, so that almost all stories & news is BAD.”

Without specifying any specific law, Trump asked this loaded question in one of the tweets: “Illegal?”

The president appeared to be referencing a recent report by a conservative blog, PJ Media, when he alleged that “96% of … results on ‘Trump News’ are from National Left-Wing Media, very dangerous.”

Google issued a statement Tuesday pushing back on his allegation.

Executives from each company will be on Capitol Hill next week to testify before a Senate panel. Members of both parties say they have ample questions for the tech honchos.

Meantime, the president again repeated his prediction that the Mexican government “ultimately” will pay for his proposed border wall.

[What to Watch in Tuesday’s Primaries]

“Yeah, the wall will be paid for very easily — by Mexico,” he told reporters in response to a question on the matter. “It’ll ultimately be paid for by Mexico.”

He did not explain why he continues to say that, given Mexican leaders have repeatedly refused.

And in a lighter moment sure to rankle his critics — some of whom say Trump often acts like a monarch — joked to the head of FIFA, the global body that oversees the World Cup soccer/football tournament that he could be serving a third term (prohibited by the Constitution) when the 2026 World cup will be held in the United States, Canada and Mexico.

“I won’t be here, he said, referring to the Oval Office. “Maybe they’ll extend the term.”