Minutes after President Obama began speaking to the country last night, one thing became very clear: He didn't have any new argument to offer Americans for why Syria needed to be punished for using chemical weapons against its own people.

In so doing, Obama violated a critical rule of politics: Don't make a big speech -- a president speaking in prime time is by default a "big" speech -- if you don't have something appropriately big to say.

So, why did President Obama give the speech? And would he have been better off not giving it at all?

Let's tackle the first question first.

Obama gave the speech because he had announced last Friday at the Group of 20 summit in Russia that he was going to address the American public on Syria.

At the time, the speech made perfect political sense. Obama needed to build the case with the American public -- and Congress -- that authorizing a military strike against Syria was the right thing to do. Using the bully pulpit -- such as it is -- was the right call since it was Obama's best chance to change minds on Syria.

But, by the time Tuesday afternoon rolled around, it had become quite clear that events had outrun Obama's plan. Congressional opposition to Obama's use-of-force resolution was on the verge on becoming overwhelming. The Russians were pushing a diplomatic solution that would require Syria to turn over its chemical weapons, a proposal of uncertain fate as Obama's speech time approached.

The speech Obama imagined last Friday simply was not adequate for the changing circumstances. And yet, Obama didn't feel comfortable enough making a new argument for the right way forward in Syria -- or he simply didn't have a new argument to make.

Given that, should he have simply canceled the speech -- noting that the situation was too fluid at the moment and that he would address the country when he could offer more definitive guidance on what would (and should) come next.

The White House and its allies dismiss such a question -- noting that while some of the arguments President Obama made Tuesday night on Syria might be old hat to the political class, they were new to many of the average Americans who tuned in to hear from their commander in chief. True enough.

And yet, Obama's speech seemed to be a patchwork of messages -- the United States isn't the world's policeman except when we can be with little risk; there is a moral obligation to punish Syria except that punishment will be decidedly limited and bound -- that may have left a skeptical public more confused about why it all mattered.

Here's the reality: Obama was in a "damned if you do, damned if you don't" situation with this speech. The changing circumstances quite clearly pointed to delaying the address, but had he done so he would have immediately been criticized for shrinking from the national stage at a critical moment in American foreign policy. In the end, he gave the Syria speech because he said he was going to -- and the speech reflected those dutiful underpinnings.