Plenty of Republicans remain bitter that their party passed that bloated $1.3 trillion omnibus—almost as bitter as President Trump, who felt pressured to sign it. But this fight doesn’t have to be over. Across Washington, principled conservatives are noodling with an idea that—if done right—could be a political winner. It’s a chance for Republicans to honor their promises of spending restraint and redeem themselves with a base turned off by the omnibus blowout. It’s an opening for the GOP to highlight the degree to which Democrats used the bill to hold the military hostage to their own domestic boondoggles. And...