President Trump, confirming Friday he is under federal investigation, continued to wage a pitched battle against the probe into Russian meddling in the 2016 election, behavior that unsettles even his Republican allies.

Trump in a morning series of Twitter posts called into question the legitimacy of the inquiry, now in the hands of special counsel Robert Mueller, the widely respected former director of the FBI. But it was the last post in that tweet storm that come back to haunt the president.

"I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt," Trump said, in what amounts to an official statement. The president's allies reacted with alarm.

"Not smart at all," a Republican member of Congress who has been a consistent supporter of Trump's said in a text message exchange with the Washington Examiner.

"The president splits his coalition when he complains about Mueller," added a Republican strategist whose clients are among Trump's cheerleaders. "He would hold it together if he'd say that the press is too focused on it and we should instead be talking about the economy and security."

Both Republicans requested anonymity because they did not want to be publicly critical of the president. Their criticism might have had an effect. On Sunday, Trump's outside legal team, hired to represent the president in the special counsel probe, insisted his tweet was not an admission that he is under federal investigation. To the contrary, attorney Jay Sekulow said.

"Let me be clear: the president is not under investigation as [former FBI Director] James Comey stated in his testimony, that the president was not the target of investigation on three different occasions," Sekulow said. "The president is not a subject or target of an investigation."

Since before being inaugurated in January, Trump has been troubled by the congressional and federal investigations into Russian meddling, calling them an attempt by Democrats and other opponents to undermine the legitimacy of his victory.

In addition to the possibility of putting himself in legal jeopardy through his tweets, Trump also is diminishing his ability to expand his base of political support.

That is unlikely to matter in solid Republican districts and "Trump Country," regions of the country that have gravitated toward the president.

"Trump supporters are solid for him no matter what he says," Bob Gleason, the former chairman of the Pennsylvania Republican Party who is close to Trump, said.

But it could cause Republicans big headaches in 2018 in the battleground seats — upscale suburban enclaves held by Republicans but won by Hillary Clinton — that could determine the fate of the House majority.

"That concerns me," Gleason conceded. "We as a party need to do much better in the Philly suburbs." He added: "But the proof — at end of day — it's not what he said, but what does he do? What are the results?"

The effect of Trump's near daily complaints has been to fire up his uncommonly loyal base, yet drive news coverage away from a legislative agenda that has shown the potential to be quite popular, including among voters who don't support him.

This week was workforce development week, capped by Trump unveiling his new Cuba policy. Last week was infrastructure week. Most of it was overshadowed by Trump's war on the Mueller investigation and carping about probes being conducted the House and Senate intelligence committees.

The president's public spats also could impact the ability of his party to deliver results in Congress.

Upcoming votes on healthcare reform, and presumably an overhaul of the federal tax code, are going to require Republicans to take significant political risks. The American Health Care Act, the GOP bill to partially repeal Obamacare, is unpopular with the broader public

Trump highlighted his 50 percent approval in the Rassumussen poll, the first time he has cracked that level since April in this survey, which tends to show him stronger than other polls.

But overall Trump's approval in the averages is stuck at 40 percent, which could imperil his agenda by making those tough votes that much tougher for Republicans looking ahead to the midterm.

"We have blinders on," a senior Republican House aide said. "We have to stay the course; we have to continue to do our work, we have to continue to move an agenda and not get distracted by leaks in investigations."

Alex Pappas contributed to this report.