WASHINGTON — The House Democratic impeachment managers began formal arguments in the Senate trial on Wednesday, presenting a meticulous and scathing case for convicting President Trump and removing him from office on charges of abuse of power and obstruction of Congress.

Representative Adam B. Schiff of California, the lead House prosecutor, took the lectern in the chamber as senators sat silently preparing to weigh Mr. Trump’s fate. Speaking in an even, measured manner, he accused the president of a corrupt scheme to pressure Ukraine for help “to cheat” in the 2020 presidential election.

Invoking the nation’s founders and their fears that a self-interested leader might subvert democracy for his own personal gain, Mr. Schiff argued that the president’s conduct was precisely what the framers of the Constitution had in mind when they devised the remedy of impeachment, one he said was “as powerful as the evil it was meant to combat.”

“If not remedied by his conviction in the Senate, and removal from office, President Trump’s abuse of his office and obstruction of Congress will permanently alter the balance of power among the branches of government,” Mr. Schiff said in his opening remarks. “The president has shown that he believes that he’s above the law and scornful of constraint.”