House Speaker Nancy Pelosi (D-Calif.) said Thursday that President Trump’s wrongdoing strikes at the heart of the Constitution and asked House committee chairs to proceed with articles of impeachment, saying lawmakers have “no choice but to act.”

Her address, in which she invoked principles espoused by the nation’s founders, came shortly after Trump went on Twitter to urge House Democrats to impeach him quickly, if they plan to do it, and suggested that he would call an expansive list of witnesses during a trial in the Republican-led Senate.

At the heart of the Democrats’ case is the allegation that Trump tried to leverage a White House meeting and military aid, sought by Ukraine in the face of Russian military aggression, to pressure President Volodymyr Zelensky to launch an investigation of former vice president Joe Biden and his son Hunter Biden, as well as a probe of an unfounded theory that Kyiv conspired with Democrats to interfere in the 2016 presidential election.

●White House gears up for aggressive effort to defend Trump in Senate as House moves toward impeachment vote.

●A look inside Trump’s anti-impeachment spin factory.

●Ukrainian lawmaker seeking Biden probe meets with Trump personal lawyer Rudolph W. Giuliani in Kyiv.