Sept. 3 (Bloomberg) -- Last time around, there were a lot of known unknowns. We were told of aluminum tubes and a mushroom cloud that only National Security Adviser Condoleezza Rice could see, and shown a picture of a white van that Vice President Dick Cheney swore to Secretary of State Colin Powell was a mobile weapons lab. President George W. Bush preferred to act before knowing the knowns rather than take the risk that actual information -- the findings of United Nations weapons inspectors -- might thwart his dream of invading Iraq to remove Saddam Hussein.

This time, we have as much certainty as you can have that the weapons of mass destruction exist, were used by Syrian President Bashar al-Assad and killed 1,500 of his citizens. We have pictures of children foaming at the mouth and bodies lined up in a makeshift morgue.

And yet, in 2003, with almost nothing to go on, Congress voted in favor of invading Iraq. In 2013, with everything to go on, it’s going to be an uphill slog to get lawmakers to approve a limited punitive strike against the Syrian government.

For President Barack Obama, the next two weeks will be harder than making it from Havana to the Florida Keys, spending days and nights alone, swimming against the tide. He’s up against a House of Representatives that doesn’t take advice or follow its leader. The 2011 military action in Libya was over without the House ever getting its act together to vote.

Default Position

The one Republican you didn’t hear crying for a congressional vote on Syria was House Speaker John Boehner. He can’t get his caucus together to vote on things that are in its interest to pass; imagine trying to herd his cats to a vote on Syria. On Tuesday, Boehner emerged from the White House to say he would support Obama and urged his colleagues to do the same. Good luck to the speaker in bringing together his hawks, who believe the president is a wimp and that we should have bombed Syria to smithereens yesterday, with his isolationists, who can’t name a war they would fight.

Part of the problem is Obama. To hurt him, his opponents are willing to hurt themselves more. Even though they had even more to gain from immigration reform than Democrats, Republicans couldn’t get a bipartisan bill to a vote in the House. And although the public will certainly blame them, many Republicans are itching to shut down the government on any pretext -- defunding Obama’s health-care law, curbing the budget, raising the debt ceiling. Stars such as Senators Ted Cruz and Rand Paul will line up to flip off the lights at the Washington Monument.

In fact, the likes of Cruz and Paul have replaced measured, politics-stops-at-the-water’s-edge Republicans such as former Senators Richard Lugar and Olympia Snowe. There’s a new breed of senator who knows everything upon arrival and is too much in a hurry to get to the Oval Office to stop and think. Obama will never get their support.

Besides ambition, add lopsided polls: A bad war has killed the tolerance of most Americans for any war. At the same time Americans overwhelmingly want Obama to consult Congress, they overwhelmingly don’t want to intervene in Syria. Taken together, you can only conclude that the public is hoping Congress stops the president.

Will there be profiles in courage -- members (such as Boehner) up for re-election in 2014 who go against their constituents? It’s more likely that even in the face of life and death, the default position of opposing the president no matter what will prevail. That’s more compelling than sending a message to the Syrian regime, which has used WMDs, and others such as Iran and North Korea that may hope to.

Even those Republicans who are in favor of action can’t agree on the kind of action to take. On Sept. 1, Senator John McCain said it would be “catastrophic” not to strike Syria but that he could only support Obama if the president committed to winning on the battlefield, forcing Assad from power and arming the Syrian rebels.

Terrible Precedent

Obama wishes for those outcomes but isn’t prepared to expose U.S. troops while trying to achieve them in the terrible crossfire of a civil (and religious) war. It’s hard to see how Obama gets straight with McCain and his close ally Senator Lindsey Graham, who in any event constitute a small bloc. Go too far in their direction, and Obama risks losing his left-wing doves and anti-interventionists/isolationists, an alliance that almost curtailed the president’s domestic-surveillance authority. Don’t go far enough, and he gives succor to the too-little, too-late caucus.

By going to Congress, Obama empowers 535 would-be commanders-in-chief who see General George Patton in the mirror each morning. But there’s also the slight chance that congressional involvement will improve the response to Syria, pushing it beyond a small strike to degrading Assad’s arsenal and arming non-jihadist rebels with sophisticated weapons without exposing U.S. troops to harm or getting mired in a Middle East conflict. We’ve done that already.

Punishing Assad may not accomplish much, but not punishing him sets a terrible precedent: that we will let pass the use of chemical weapons. Even though the something to be done isn’t perfect, something is sometimes all you can get.

(Margaret Carlson is a Bloomberg View columnist.)

To contact the writer of this article: Margaret Carlson at mcarlson3@bloomberg.net.

To contact the editor responsible for this article: Max Berley at mberley@bloomberg.net.