President Donald Trump’s behavior left House Speaker Nancy Pelosi no choice but to open the fourth impeachment inquiry in the nation’s history.

Congress and the country cannot ignore actions by Trump that have come to light in the past two weeks. They cannot ignore White House stonewalling that eased only after Pelosi, D-Calif., announced the formal investigation.

Pelosi had for months resisted calls for an impeachment inquiry. But for Pelosi, and for us, the latest revelations about Trump’s pressuring of a foreign government to investigate his political rival crossed a line, making it essential that the House launch a formal impeachment inquiry. After more than two years of national discussion about protecting our elections from foreign influence, the president — personally — solicited outside interference.

As Ukraine President Volodymyr Zelensky requested U.S. assistance to help fend off Russian aggression, Trump replied by pressing for a foreign investigation of unsubstantiated allegations about former Vice President Joe Biden. It’s all there in the reconstructed transcript, released last week, of the July 25 conversation between the two men.

Trump and his allies claim that the president never expressed a clear quid pro quo in his conversation with Zelensky. But Trump didn’t need to explicitly say what was obvious — that Ukraine needs our nation’s support and protection if it has any hope of survival. What Trump didn’t tell Zelensky was that he was blocking $391 million of security assistance for the country. But, according to the intelligence officer who blew the whistle on Trump’s action, Ukrainian leaders understood that they needed to show willingness to “play ball” before Trump would even talk to Zelensky.

Has Trump gone too far? Has he committed an impeachable offense? Do his actions constitute “high crimes and misdemeanors?” Ultimately that’s a question the U.S. House must decide as it determines whether to impeach him — and for the Senate to determine if it tries him.

Before they and the nation try to answer that question, the president’s actions must be thoroughly investigated.

The president’s behavior is, as U.S. Sen. Mitt Romney, R-Utah, put it, “deeply troubling.”