Republican leaders are trying to sound as confident as they can that the Obamacare replacement bill will pass the House today. But there's an air of nervousness in their voices, and they're not even willing to entertain questions about what happens if it fails. Here's House Energy and Commerce Committee chairman Greg Walden a few minutes ago, just after the Rules Committee approved the rule for the floor debate:

• Me: The White House says there's no Plan B, but what if —
• Walden: "We're going to win on the floor today."
• To another reporter who tried the same question: "We're going to pass the bill. I'm not going down that path."

Why do they think the votes will come together? "The president recognizes that the success of this will have a lot to do with the future of his presidency, and I think the members recognize that too," House Rules Committee chairman Pete Sessions told me.