As President Donald Trump attempts to muscle his GOP agenda through a narrow House majority, Rep. Chip Roy is perhaps the most important holdout to win over. He may also be the toughest. Speaker Mike Johnson and his team have been confident they can pass Trump’s massive reconciliation bill, because they don’t believe any Republican will want to stand in the way and face Trump’s wrath. But Roy, the unapologetic fiscal hawk, is the rare GOP lawmaker willing to publicly challenge the president. He has already survived multiple calls by his own party to oust him — including from Trump...