Democrats demurred on Sunday on whether Donald Trump has committed impeachable offenses after he was implicated last week in a potential crime, but promised vigorous investigations if the party takes control of the U.S. House in the midterm elections.

"The role of Congress is not to protect the president," Rep. Jerrold Nadler of New York said on NBC's "Meet the Press." "It's to ... hold the president and any president accountable to the American people." Nadler is the top Democrat on the House Judiciary Committee, which would hold any impeachment hearings.

His comments came after a week of increasing chatter about how or when Congress will judge whether the president's conduct meets the threshold for impeachment. In his Aug. 21 guilty plea to campaign finance violations, Michael Cohen, Trump's former lawyer and "fixer," implicated the president in off-the-books hush money paid to a porn star. Paul Manafort, Trump's former campaign manager, was found guilty the same day of bank and tax-fraud charges.