WASHINGTON — When Representative Tim Murphy was accused of pressing his mistress to have an abortion, the Pennsylvania Republican apparently crossed a line that could not be tolerated in his party. Speaker Paul D. Ryan encouraged him to resign, and he was gone from the House in a day.

That was in October. Last Friday, Representative Blake Farenthold, another Republican, was unmasked as the lawmaker who used $84,000 in taxpayer funds to secretly settle a lurid sexual harassment case, but Mr. Ryan has been silent on his future.

On the same day, Representative Ruben Kihuen, a relatively unknown Democrat, was accused of propositioning his campaign finance director for sex despite her protestations. Within hours, Representative Nancy Pelosi, the Democratic leader, demanded his resignation, most likely dooming the political career of a rising star who won a swing district in Nevada just last year.

And on Tuesday, Representative John Conyers Jr.’s stature as the longest serving African-American man in House history came to an ignominious end. Following a concerted push for his resignation after several aides accused him of harassment, Mr. Conyers, 88, announced he would leave the House immediately.