Buchanan was a long time opponent of the globalist agenda of both Bushes.
It doesn't have anything to do with republicans and democrats, it has to do with foreign policy doctrines.
In the GOP there are Realists, NeoCons, and Isolationists.
In the dem party there are Realists, Liberal Interventionists(sometimes called liberal internationalists), and Antiwar Pacifists.
Among these rightwing isolationists, there are two groups. First there are the libertarian minded such as Senators Paul and Lee. Ron Paul also is/was in this group. The second group are those that are called PaleoCons, PaleoPopulists, or Goldenagers. These are people like Buchanan and Taki. You can get a good idea of their foreign policy at The American Conservative or Taki's mag.
The Antiwar Pacifist dems are people like Sens Wyden and Udall. You can get an idea of their foreign policy at Antiwar.com
Now these antiwarriors and isolationists have very little influence on US Foreign Policy. They are never given jobs on a prez's(R or D) foreign policy team. They are never allowed to chair a congressional committee that has any thing to do with foreign policy. But they can serve on those committees. Rand Paul, Dems Wyden and Udall serve on the Senate Foreign Policy Committee.
So it is the Realists(R&D), the Neocons(R), and Liberal Interventionists(D) that control foreign policy. A GOP prez's foreign policy team will be made up of Realists and NeoCons. A dem prez has Realists and Liberal Interventionists on his foreign policy team. For example: A dem prez always has a Realist at SoD, Republican Realist Gates, Dem Realist Panetta, and Republican Realist Hagel. A dem prez always has an interventionist at SoS, Kerry and Clinton. A republican prez usually has a realist at SoS: Rice, Powell, Baker, Schultz, Haig, Kissinger. A Gop prez usually has a NeoCon at SoD: Rumsfeld, Cheney, Wienberger, Rumsfeld
So, now lets look at Syria.
The first thing you need to understands is that Obama has never wanted to intervene in Syria. Because he learned his lesson in Libya when the Italians and Brits didn't come through plus public opinion is against it.
He never had to worry about it because thruout 2011 and 2012 the Realists were opposed to intervening. But beginning in late 2012 the Realists began to gradually shift so by may 2013, most realists were supporting intervention.
On May 22 the Senate Foreign Relations Committee took a vote on whether or not to intervene in Syria. There were 15 R&D votes to intervene and two dems(Wyden and Udall) and one republican(Randy Paul) opposed. 15 Realists, NeoCons, and Interventionists versus 3 antiwar pacifists and isolationists. Not long after that Mike Lee(isolationist) joined the other 3 to submit legislation into the Senate opposing the intervention .
What about the whole senate? They won't take a vote but if they did, it would be to intervene.
What about the House? Amongst the dems, there would be relatively more pacifists than the are in the Senate and among the GOP there would relatively more isolationists than in the Senate. I figure 80-120 votes total in the House opposed to intervening in Syria.
You can forget about Congress stopping Obama because Congress is pushing Obama. He ain't got nowhere to hide and he can't hide behind the pacifists and the isolationists.
And some of these hardcore NeoCons are not going to be satisfied with cruise missles. They want a no fly zone and boots on the ground. The could care less about a multilateral coalition and prefer unilateralism.