Pelosi comes under fire regularly from progressives because of her reluctance to pursue impeachment of the president. She appears to prefer an approach of conducting as many investigations of Trump and his administration as possible — seemingly in hopes that a steady drip of ugly information about the president will convince voters to do the right thing and turn him out of office in 2020.

But that approach won’t work if Trump can shrug off Congress without consequence — or slow-walk oversight efforts until after the election.

Pelosi, though, is never stronger than when defending the rights of the House of Representatives. Remember: She brought Trump to heel earlier this year, refusing him a venue for the State of the Union speech until he brought an end to the government shutdown over his request for border wall funding. It was the best moment thus far of Pelosi’s second stint as speaker.

If Barr continues to refuse to testify, Pelosi will be faced with two choices: She can let it go, and accept that Trump will be impervious to any kind of accountability for the remainder of his presidency. Or the House she leads can impose consequences.