WASHINGTON (AP) — The combative White House letter vowing to defy the “illegitimate” impeachment inquiry has actually put President Donald Trump on a more certain path to charges. His refusal to honor subpoenas or allow testimony would likely play into a formal accusation against him.

The letter sent to House leaders by White House Counsel Pat Cipollone Tuesday evening declared the president would not cooperate with the investigation — a clear reason, Democrats say, to write an article of impeachment charging him with obstruction.

The White House insists that a formal House vote is necessary just to start the impeachment process. But Democrats are moving ahead without one, confident for now that they are backed by the Constitution and Trump’s own acknowledgements of trying to persuade a foreign government to investigate a political foe.

“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,” said House Speaker Nancy Pelosi in response to the letter. “Mr. President, you are not above the law. You will be held accountable.”

Trump again defended his decision not to cooperate, calling a whistleblower’s complaint about his call with Ukraine’s leader “a fraud being perpetrated on the American public” and saying Republicans are being treated unfairly. He repeated he was being vilified for “a perfect phone call.”

But the president also undercut his no-cooperation argument Wednesday by putting conditions on his willingness, saying he would cooperate only if the House held a vote and Democrats would “give us our rights.”

Bolstered by polls showing increased public support for impeachment, Pelosi has shown no signs of shifting her strategy. Democrats plan to continue investigating while focusing on the president’s own acknowledgements that he asked Ukrainian President Volodymyr Zelenskiy to investigate his country’s involvement in the 2016 presidential election and also political rival Joe Biden and his family.

“The evidence provided by the president and his people has already been overwhelming,” even without additional witness testimony, said Connecticut Rep. Jim Himes. Himes is a Democratic member of the House intelligence committee, which is leading the Ukraine investigation.

The intelligence panel, along with the Foreign Affairs and Oversight and Government Reform panels, subpoenaed Gordon Sondland, the U.S. European Union ambassador, on Tuesday after Trump’s State Department barred him from showing up at a scheduled deposition. Texts provided by another diplomat last week showed Sondland and others navigating Trump’s demands for investigations as they spoke to Ukrainian government officials about a possible visit to Washington.