The NeoCon Republicans were the first to want to intervene in Libya. The Realist Republicans opposed. Bob Gates, Henry Kissinger, and James Baker very publicly opposed. It was only after the Liberal Interventionist democrats negotiated the multilateral agreement that Obama intervened. The multilateral agreement was set up by Susan Rice, Samantha Power, and Hillary.
The NeoCons praised Obama for intervening. Bill Kristol proclaimed Obama to be a "Born Again NeoCon". Of course they criticized him too, saying he should have gone in immediately instead of waiting for the multilateral agreement. And since Obama went in multilaterally, they complained he was leading from behind. Hardcore NeoCon John Bolton complained because Obama didn't put boots on the ground in Libya.
As for arming the Syrian rebels, look at the Senate Foreign Relations Committee vote to arm the rebels in May of 2013. That passed the committee 15 to 3. The NeoCons(R), the Realists(R & D), and the liberal interventionists(D) voted yes. The 3 no votes were the 2 antiwar dems(Udall and Murphy) plus the GOP isolationist Randy Paul. After that vote, Mike Lee joined Paul, Udall, and Murphy on legislation to block the arming.
Its not about a Republican versus Democrat. Its about NeoCons, Realists, and Liberal Interventionists.
On the recent issue of imposing additional sanctions on Iran before the negotiations played out, The NeoCons(led by Sen Kirk) and the Liberal Interventionists(led by Sen Menendez) wanted the additional sanctions. The Realists led by Sen Feinstein(D) and Sen Corker(R) opposed the additional sanctions. The antiwar dems and GOP isolationists also opposed the sanctions.
Neocons and Liberal Interventionists usually differ only in rhetoric (liberal interventionists tend to use more "humanitarian" sugar-coat for their crusades, but there's plenty of overlap here), not in substance. Both hark back to the Wilsonian tradition.
Come to think of it, most neocons are closer to liberals on a whole host of issues, from support for the welfare state (albeit less "wasteful") to support for liberal immigration policy than they do with traditional conservatives. Makes you wonder why neoconservatives don't just go back to the Democratic party where they belong and leave the GOP to the realists and libertarians.
PS - Which prominent Democrats are foreign policy realists? It seems to me that Democrats are either Wilsonian internationalists (the majority) or George McGovern-style pacifists (mostly a thing of the past). The only really prominent Democratic realist who comes to mind is the aging Zbiegnew Brzezinski. In contrast, in the GOP you have Wilsonian internationalists (neocons), realists (Reaganites), and “isolationists” (libertarians, paleoconservatives).