Last but not least: if Democrats give in to the blackmailers now, they’ll just face more demands in the future. As long as Republicans believe that Mr. Obama will do anything to avoid short-term pain, they’ll have every incentive to keep taking hostages. If the president will endanger America’s fiscal future to avoid a tax increase, what will he give to avoid a government shutdown?

So Mr. Obama should draw a line in the sand, right here, right now. If Republicans hold out, and taxes go up, he should tell the nation the truth, and denounce the blackmail attempt for what it is.

Yes, letting taxes go up would be politically risky. But giving in would be risky, too — especially for a president whom voters are starting to write off as a man too timid to take a stand. Now is the time for him to prove them wrong.