Rand Paul's marathon, talk-til-you-drop filibuster has thrown Congress for a loop. The Kentucky senator's impassioned defense of civil liberties has jumbled the customary partisan lines, earning him enemies and allies alike from unexpected quarters. Liberals are dismayed that only one Democrat — Ron Wyden of Oregon — joined Paul in condemning Attorney General Eric Holder's suggestion that the president could, in certain circumstances, use a drone to target an American citizen on U.S. soil. Conservatives, on the other hand, have taken Paul to task for being naive and soft on defense.

That even the most liberal Democrats would hesitate to join Paul can be easily rationalized on a political level. President Obama has been having a tough time getting his nominees confirmed, and Democrats would surely not want to lend any legitimacy to the types of Republican stalling tactics that turned Chuck Hagel's recent confirmation process into a seemingly endless nightmare. It's certainly true, too, that Democrats have toned down the robust civil liberties rhetoric that partly defined their opposition to President Bush, again out of deference to a Democratic president who has ramped up some of Bush's counterterrorism policies while phasing out others.

But the Democratic Party has long been divided between hawks and doves — one need look no further than the 2008 primary between Obama and Hillary Clinton, which partly hinged on Clinton's support for the Iraq War. 

The Republican response to Paul, however, is the latest evidence of something new: A deep, growing rift within the GOP over national security, pitting establishment defense hawks against quasi-isolationists, led most prominently by Paul. These insurgents have broken the traditional mold of Republican defense policy in several areas, such as emphasizing civil liberties over security and calling for cuts to Pentagon spending.

Indeed, the Republican criticism of Paul's speech smacks of the old guard talking down to an upstart. "If Mr. Paul wants to be taken seriously he needs to to do more than pull political stunts that fire up impressionable libertarian kids," Sen. John McCain (R-Ariz.) said on the Senate floor today. Paul's assertion that the president could target random, innocent Americans, such as Jane Fonda for her opposition to the Vietnam War, had thrust the debate into the "realm of the ridiculous," McCain continued. 

Sen. Lindsey Graham (R-S.C.), another defense hawk, even suggested that the group of Republicans who joined Paul were inspired by pure partisan motives. "I don't remember any of you fellow Republicans coming down here and saying President Bush was going to kill anyone with a drone," Graham said. "But we had a drone program back then... so what is it that's got you so spun up now?"

The divide is also evident in conservative media. The Wall Street Journal editorial board admonished Paul, saying:

Calm down, Senator. Mr. Holder is right, even if he doesn't explain the law very well. The U.S. government cannot randomly target American citizens on U.S. soil or anywhere else. What it can do under the laws of war is target an "enemy combatant" anywhere at anytime, including on U.S. soil. This includes a U.S. citizen who is also an enemy combatant. The President can designate such a combatant if he belongs to an entity — a government, say, or a terrorist network like al Qaeda — that has taken up arms against the United States as part of an internationally recognized armed conflict. That does not include Hanoi Jane. [Wall Street Journal]

National Review correspondent Kevin D. Williamson, on the other hand, full-throatedly endorsed Paul's position:

Senator Paul is right to take this opportunity to, as somebody once put it, stand athwart, yelling "Stop!" Senator Ted Cruz and others are right to encourage him in this. If your government can put you to death without trial — not on the field of battle, but at breakfast — then you are not a citizen at all: You are a subject. And Americans were not born to be subjects. [National Review]

While voters may be more accustomed to seeing the GOP work in lockstep on national security, the divide is more likely to sharpen. Obama's embrace of lethal counterterrorism tactics, with its accompanying interpretation of broad executive power, is bound to draw more GOP criticism as Republicans seek to carve out some space on national security. Paul's speech also marks another trend: A growing distance between Republicans and the foreign policy legacy of the Bush administration.