Tax reform is a worthwhile policy goal, and Mr. Boehner is right to pursue it. But the only way he can avoid being taken for a ride by Democrats is if all parts of any deal are negotiated, voted on and then implemented immediately. Two men, one deal, once. Promises of future action aren’t credible.

Even if Mr. Obama is sincere on tax reform, he can’t guarantee he can deliver Senate Democrats who are desperate to keep their majority in 2012, much less Nancy Pelosi. We’re told that in Thursday’s White House meeting, Mr. Obama promised to veto any short-term debt-limit deal to give the two sides more time to negotiate. If that’s true, then the President isn’t serious. It means he is using the pressure of the August 2 deadline to bull-rush Mr. Boehner into a bad deal.

If Mr. Obama is sincere about a long-term spending and tax reform agreement, he’ll take the time to get it right. If he insists on issuing ultimatums, then House Republicans would be better off passing a debt-limit ceiling for a few months with comparable spending cuts and letting Senate Democrats do the same. Mr. Boehner shouldn’t bet his majority on Mr. Obama’s promises.