The decision to block Gordon D. Sondland, the United States ambassador to the European Union, from speaking with investigators is certain to provoke an immediate conflict with potentially profound consequences for the White House and President Trump. House Democrats have repeatedly warned that if the administration tries to interfere with their investigation, it will be construed as obstruction, a charge they see as potentially worthy of impeachment.

But in making the decision on Tuesday, hours before he was scheduled to sit for a deposition in the basement of the Capitol, the Trump administration appears to be making the calculation that it is better off risking the House’s ire than letting Mr. Sondland show up and set a precedent for cooperation with an inquiry they have strenuously argued is illegitimate.