Stephen Colbert spent nine years mocking conservatives on a comedy program premised on mocking conservatives. It was a good fit; Colbert’s political views lean left, and even after leaving his right-wing loudmouth character behind, he’s been happy to dive into the most contentious political issues of the day. (Just watch the video he made in June celebrating the Supreme Court gay marriage decision and deriding its dissenters.)

On Tuesday night, the new play-it-straight Colbert had Donald Trump as a guest. The night before, he had Ted Cruz. On his September 8 premiere, he had Jeb Bush. The appearances raised questions for Republicans considering future appearances. Is Colbert really playing it straight? And is it worth appearing on his program?