When Jeff Flake of Arizona announced his retirement from the Senate last fall, he become one of the strongest Republican critics of President Trump. “I rise today to say, ‘Enough,’ he told his colleagues, ripping the president of his party for policies and behavior he called “dangerous to a democracy.” Last month, Flake delivered a second Senate floor speech likening Trump’s words to those of 20th century Russian dictator Josef Stalin. As he leaves his Senate seat, he has pointedly declined to rule out challenging Trump by running for president himself. Yet he has not waged an all-out assault on the president’s agenda. He joined fellow Republicans in delivering Trump’s greatest victory so far, backing the $1.5-trillion tax cut despite his own expressed concerns about budget deficits. We met in his office – that doubles as his living quarters when he’s in Washington – to discuss his approach to challenging this White House, and his future plans.