President Donald Trump on Thursday said he might sue to halt House Democrats’ impeachment inquiry and lashed out at Intelligence Chairman Adam B. Schiff as he struggled to fashion a counter-message.

The president headed to the Oval Office after he returned to the White House for the first time since the inquiry began, and used Twitter to attack Schiff. So far, his strategy has mostly been to hammer Speaker Nancy Pelosi and the chairman with his usual volley of insults and allegations, while trying to discredit all involved.

Trump criticized the intelligence community whistleblower whose complaint pushed Pelosi to move ahead with impeachment for basing his alarms on “only … second hand information.” He also questioned how Schiff can call that individual “credible” when the whistleblower possessed “zero info” and had a “known bias.”

But the latter statement raises questions because the president has said he does not know who the whistleblower is.

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Liddle’ Adam Schiff, who has worked unsuccessfully for 3 years to hurt the Republican Party and President, has just said that the Whistleblower, even though he or she only had second hand information, “is credible.” How can that be with zero info and a known bias. Democrat Scam!

— Donald J. Trump (@realDonaldTrump) September 26, 2019

“It shouldn’t be allowed. There should be a way of stopping it. Maybe legally through the courts,” he told reporters at Joint Base Andrews as he returned to Washington from New York.

The president did not explain what legal rationale any sitting commander in chief would have to stop an impeachment inquiry. The monarchy-weary authors of the Constitution deemed a mechanism to remove a president over misconduct or an abuse of power so important they included it in the country’s founding document.

[Whistleblower describes White House trying to cover up Ukraine phone call]

“The President, Vice President and all Civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors,” states Article II of the Constitution.

Senior Democrats, including Pelosi, in recent days have suggested the president at times has behaved like “a king.”

Trump’s comments came at Joint Base Andrews as he returned from morning fundraisers in New York that capped his three-day visit there for an United Nations General Assembly session.

After Marine One landed on the White House’s South Lawn, Trump greeted a group of supporters but only waved to a large throng of reporters who had ample questions about House Democrats’ impeachment inquiry and his July 25 call with Ukraine’s new president on which the probe is largely centered.

On Wednesday, Schiff told reporters a White House-produced summary of that call — in which Trump asked his counterpart for “a favor” of an investigation of 2020 Democratic candidate Joe Biden — showed “a classic mafia-like shakedown of a foreign leader.” That’s because Trump also told Volodymyr Zelenskiy that the United States has been “very, very good” to his country but the relationship was not “reciprocal.”

Around the same time as his ask, the president personally held up a $250 million military aid package to Ukraine that Congress had approved with wide bipartisan support as Republicans and Democrats were eager to help the Eastern European country defend against further Russian aggression.

Trump had tough words for the Intelligence Committee chairman as he spoke loudly over Air Force One’s engines, his signature animated cadence back in his voice after a flat performance during a General Assembly-wrapping press conference on Wednesday.

“I just watched a little of the news on TV. It’s a disgrace,” he said to reporters.

“Democrats are going lose the election and they know it. That’s why they are doing it,” Trump said, then declaring the impeachment inquiry — which Pelosi resisted until more and more details of the July 25 call seeped out — “should never be allowed.”

“I have to put up with Adam Schiff on an absolutely perfect phone call with the new president of Ukraine,” the president said. “But Adam Schiff doesn’t talk about Joe Biden and his son walking away with millions of dollars from Ukraine, and then millions of dollars from China.”

The president and White House have yet to provide evidence for his claims that then-Vice President Joe Biden used his influence with the previous Ukrainian government to shut down a probe of a company that employed one of his sons, Hunter Biden. Nor have they showed any evidence to support his allegations that the Biden son nefariously got paid in either country.

[Intel chief calls whistleblower complaint ‘unprecedented’]

Trump’s comments at Andrews and ducking the White House press corps as he headed to the Oval Office, along with his uncharacteristically bland and meandering Wednesday afternoon new conference, suggest a chief executive searching for a strategy to counter House Democrats’ impeachment narrative.

He began the second full day of the inquiry as he often does, on Twitter. He fired off a list of re-tweets, sharing with his followers tweets from those in his inner circle, including his children, Vice President Mike Pence, and supportive Fox News guests.

The president on Wednesday struggled to answer a CNBC reporter’s question about how his ask of Zelenskiy to essentially interfere in an U.S. election was appropriate. His answer was disjointed and at times incoherent.

“Look, that whole witch hunt was started, and hopefully that’ll all come out. But there’s been some fantastic books written that just came out – whether you will look at Gregg Jarrett, or [Andrew C.] McCarthy’s book that just … came out recently, and so many other books. And a lot of books are coming out,” he said, then veering off about a group of Democratic senators’ and Joe Biden’s shared concern about corruption inside Ukraine.

The next morning, Trump and his top aides showed no signs of having crafted a strategy to counter the impeachment inquiry and Democrats’ charges he broke federal law by seeking a personal political benefit from a foreign government.

“A whistleblower with second hand information? Another Fake News Story!” he tweeted from Trump Tower in Manhattan. “See what was said on the very nice, no pressure, call. Another Witch Hunt!”

A whistleblower with second hand information? Another Fake News Story! See what was said on the very nice, no pressure, call. Another Witch Hunt!

— Donald J. Trump (@realDonaldTrump) September 26, 2019

Pelosi made clear he and his team will have plenty of time to come up with a strategy and message.

“There are some in our caucus who think, ‘Let’s just have an impeachment,’” she told reporters Thursday. “No, we have to have an inquiry. … There is no rush to judgment.”

Lindsey McPherson and John M. Donnelly contributed to this report.