Not being as eloquent as most of the previous posters, just wanting to add a little more fuel of a different type to the fire:

As known:

01 The American people are not in support of "POTUS's Great Adventure". And it's not even close. The polls are showing that simple fact. It's Not Even Close

02 Congress is not on board. When leadership on both sides comes out in favor, but they're not willing to push on their membership to follow their lead, that's a 'tell' in that each member gets to make up their own mind, and so far, it's a rout.

03 The economics of this could totally blow up in our face:

According to the U.S. Treasury, foreigners now hold approximately 5.6 trillion dollars of our debt. Over the past couple of decades, the proportion of our debt owned by foreigners has grown tremendously, and today we very heavily depend on nations such as China to buy our debt.

At this point, China owns approximately 1.275 trillion dollars of our debt, and Russia owns approximately 138 billion dollars of our debt.

So what would happen if China, Russia and other foreign buyers of our debt all of a sudden quit purchasing our debt and instead started dumping the debt that they already own back on to the market?

In a word, it would be disastrous.

As has been written about previously, the U.S. government will borrow about 4 trillion dollars this year.

Close to a trillion of that is new borrowing, and about three trillion of that is rolling over existing debt.

If China and other big foreign lenders quit buying our debt and started dumping what they already hold, that would send yields on U.S. Treasuries absolutely soaring.
Better think long and hard about the economics

04 Lastly, I'm starting to wonder how much of this is really still about Syria, and how much of this has become a pissing contest between the US and Russia/China?

If it's become more about Russia/China, then POTUS needs to step back and re-assess his strategy (assuming a coherent one exists).