Congressional Democrats are in a bind. If they vote to authorize a military strike on Syria, they could be putting the country on a slippery slope to war. But if they vote no, they will deliver a crushing defeat to their president.

What President Barack Obama did was call their bluff. Last week, more than 50 House Democrats signed a letter urging the president to “seek an affirmative decision of Congress” before committing to any military engagement. That was the Democrats’ way of going on record to express reservations about what Obama sounded like he was going to do anyway. Then, lo and behold, the president decided to do exactly what they asked. Now it’s their decision.

Anti-war sentiment is a powerful force on the left. It was nurtured by bitter experiences in Vietnam and Iraq. Obama himself comes out of that tradition. He is trying to keep faith with it by arguing, as he did at a meeting with congressional leaders, that his attack plan is “proportional, it is limited, it does not involve boots on the ground.” He added, “This is not Iraq, and this is not Afghanistan.” Secretary of State John Kerry tried to change the metaphor when he called it “a Munich moment.” Meaning, a “no” vote would be a vote to appease a dictator.

The president cannot afford to lose this vote. If he does, his authority will be severely weakened. He will find it difficult to get anything passed for the remainder of his term — budget deal, immigration reform, funding for Obamacare, climate change legislation. He will instantly become a lame duck.

To win, Obama needs to carry a solid majority of Democrats. Most Republicans will vote no. A lot of Tea Party Republicans want to use the vote to bring Obama down. Rather than debate the policy, they will argue that this president is simply not competent to carry it out. They don’t believe he should be given war-making powers. If Obama can’t keep his own party behind him, Republicans are not going to bail him out.