MONTGOMERY, Ala. — Alabama Gov. Robert Bentley resigned Monday rather than face impeachment and pleaded guilty to two misdemeanor campaign violations that arose during an investigation of his alleged affair with a top aide.

In a remarkable fall, the mild-mannered 74-year-old Republican and one-time Baptist deacon stepped down as the sex-tinged scandal gathered force over the past few days.

Legislators turned up the pressure by opening impeachment hearings Monday. Last week, the Alabama Ethics Commission cited evidence that Bentley broke state ethics and campaign laws and referred the matter to prosecutors.

“There’ve been times that I let you and our people down, and I’m sorry for that,” Bentley said in the old House chamber of Alabama’s Capitol after he pleaded guilty.

The violations were discovered during the investigation of his affair but were not directly related to it.

In court, Bentley appeared sullen and looked down at the floor. He stood up and said “yes, sir” in a gravelly voice as the judge read out the charges he was pleading guilty to.