“The [White House] letter isn’t an argument, it’s a diatribe. And it reflects what is a clear decision by the White House – obstruct, deny, stonewall,” Rep. Peter Welch (D-Vt.) said in an interview. “I think it would be a basis for proceeding but that doesn’t answer the question: Is it the time to proceed. Is the public there?”

Senior Democratic aides insisted lawmakers are still “finding the facts” and not seriously talking about writing specific articles of impeachment at this time, in part because Democrats are continuing to gather evidence against Trump. But Democrats readily agree that Trump’s blanket stonewalling of their investigations has veered into impeachable territory.

“There is a lot of evidence that is just staring us in the face,” said Rep. Val Demings (D-Fla.), a member of the House Judiciary and Intelligence Committees who has argued since April that Democrats have enough evidence to impeach Trump.

Trump has overseen efforts to defy House subpoenas for documents and testimony related to former special counsel Robert Mueller’s investigation of his campaign’s ties to Russia. Trump’s Treasury Department has refused to turn over his tax returns, despite a law permitting some lawmakers to obtain them. And Trump has helped scuttle other committees’ investigations of his alleged campaign finance violations, offers of pardons to immigration officials, administration officials’ use of private email for government business and political interference in the U.S. census.

And just this week, Trump blocked a key witness in the House’s expanding investigation into Trump’s effort to pressure Ukrainian President Volodymyr Zelensky to investigate former vice president and 2020 rival Joe Biden.

“This total obstruction is a stand-alone basis for impeachment,” said Rep. Lloyd Doggett (D-Texas) on Twitter. “The House should proceed as soon as possible to impeach this lawless president and wannabe authoritarian.”

In the White House letter, Cipollone took potshots at top Democrats running the impeachment probe and blasted them over the House procedures.

“In order to fulfill his duties to the American people, the Constitution, the Executive Branch, and all future occupants of the Office of the Presidency, President Trump and his Administration cannot participate in your partisan and unconstitutional inquiry under these circumstances,“ Cipollone wrote.

In response, Pelosi sent her strongest signal yet that she views Trump’s resistance as an impeachable offense.

“The White House should be warned that continued efforts to hide the truth of the President’s abuse of power from the American people will be regarded as further evidence of obstruction,” she said in a statement. “Mr. President, you are not above the law. You will be held accountable.”

But many top Democrats are also wary of building their entire case for impeachment around obstruction of Congress. Rather, they’d prefer it to be the secondary issue in a larger set of articles that focus on alleged abuse of power by Trump, primarily by pressing Ukraine to probe Biden and his son Hunter.

“We still have to stay very focused and talk to fact witnesses who just seem to be lining up,” Demings cautioned. “We have to continue to do a very methodical, a very thorough and complete investigation.”

It was Trump’s conduct toward Ukraine that united the Democratic Caucus behind formal impeachment proceedings and the issue that drew Pelosi — and an increasing share of voters across the country — to support taking that step.

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Democratic leaders believe Trump’s efforts to solicit Ukraine’s interference in the next election tells a compelling and cogent story to voters about Trump’s mishandling of national security and willingness to sacrifice it to boost his own political prospects. They’ve already received documents and testimony from a central witness in the episode, former Ambassador Kurt Volker, and they’ve obtained a whistleblower’s complaint on the matter that was deemed by an intelligence community watchdog as “credible” and “urgent.”

Many Democrats are confident that other information on Trump’s handling of Ukraine will reach Congress even if Trump attempts to thwart it.

Obstruction, on the other hand, is more complicated to explain — and Trump has spent months fending off allegations that he attempted to obstruct the special counsel’s probe of his campaign’s ties to Russia.

Yet indications that the House is coalescing around an obstruction of Congress charge against Trump abound. The House’s top lawyer, Doug Letter, told a federal judge Tuesday that an obstruction article is under serious consideration. And after the White House released its letter this week, other members of Pelosi’s leadership team ramped up their attacks on Trump for flouting their subpoenas and information requests.

“This President is not above the law,” tweeted the House’s No. 3 Democrat, Rep. Jim Clyburn of South Carolina. “His refusal to comply with House subpoenas in our impeachment inquiry is another unlawful attempt to hide the facts.”

Rep. John Yarmuth (D-Ky.) said in an interview that Trump’s refusal to cooperate is fueling multiple potential obstruction charges.

“If they keep stonewalling,” Yarmuth said, “the committee’s going to say we’ve got enough for another obstruction case.”

Sarah Ferris and Andrew Desiderio contributed to this report.

