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The cost of President Obama’s proposed air war against Syrian government forces could quickly run into the tens of billions of dollars. Not enormous for a government that spends more than $700 billion a year on military matters, but not chump change either.

Given the fact that the Pentagon is bracing for a $20 billion reduction in funding as delayed spending caps from the 2011 debt-ceiling deal – what Washington calls “sequestration” – kick in next month, one might think that hawks would be expressing concerns about such triggering such costs.

But it’s been quite the contrary. The hawkiest of them all, Sen. John McCain, has been pushing longer and harder for American intervention in the Syrian civil war than anyone else. But he has also been among the most outspoken opponents of sequestration, arguing that the across-the-board caps on deficit spending that Republicans fought to preserve are not worth the damage to American military readiness.

To the interventionists in both parties, there’s no contradiction. They believe that the military should be expanding its global footprint and that America ought to have long ago been blowing up billions of dollars worth of Boeing’s best ordnance in Syria.

Syria is evidence to them of the need to expand, not contract, spending. And Republicans, having been the party in favor of increased military spending for most of the past 30 years, might be expected to broadly agree.

Sequestration, though, has been quite instructive on the new GOP. What was conceived by Obama’s team as a way to force Republicans to accept higher taxes – a punishment – has turned out to be rather popular on the right. While Democrats were aghast at any goring of their sacred cows on welfare and other domestic spending, Republicans have been mostly sanguine about capping costs at the Pentagon. This has been a great frustration to the president and to old-guard Republicans. In the post-Iraq Republican Party, though, there has been a marked return to the GOP’s anti-intervention roots.

But there are limits.

House Republicans won an extension of the sequestration during the last bout of fiscal cliff jumping in the spring. As part of the deal to keep the caps, the Pentagon was given some leverage to shift obligations and defer painful choices. Well, time’s up. And Democrats are ready to pounce.

In mid-August, the ranking Democrat on the House Budget Committee, Rep. Chris Van Hollen, D-Md., laid out his plan for the looming fiscal fight. In interviews, Van Hollen made clear that Democrats saw the deferred Pentagon pain as a point of leverage. As he told the Washington Post at the time: “If Republicans want to relieve the $20 billion cut to Defense, we must increase non-Defense spending by $20 billion.”

Democrats may be hard pressed to refuse their president’s call to arms in Syria, but that doesn’t mean they will just pony up the extra costs without getting something for, as Obama likes to say, “nation building here at home.”

The calls for squelching the sequestration for the sake of a Syria strike have begun. We’ve heard from Obama’s former Pentagon boss, Leon Panetta, as well as House Armed Services Committee Chairman Buck McKeon about the Syria-sequestration nexus. As we get closer to the missiles flying, we will hear more as the military makes its case for a return to full funding.

As Republicans consider whether to back Obama’s call for a Syria attack, they will also be thinking about the political battles here at home. Liberals were already calling the deferred Defense cuts the Democrats’ “ace in the hole.” That hole card will get only more valuable if the military has to spend billions more on another Middle East war.

Chris Stirewalt is digital politics editor for Fox News. Want his daily political newsletter, FOX News First in your inbox? Sign up here. To catch Chris live online daily at 11:30 a.m. ET, click here