One of the traditional roles for a presidential running mate is a willingness — and ideally, a propensity — to be an “attack dog,” going after the rival party and saying the things the candidate would say, if he or she wasn’t trying to appear above the fray.

It’s probably too soon to talk too seriously about Joe Biden’s chances of making the ticket, but if he’s auditioning for the part, and hoping to prove himself as a sufficiently aggressive pugilist, I think he’s doing an awfully good job.

We learned this week, for example, that John McCain has completely reversed course on the White House’s authority to conduct warrantless searches of Americans’ phone calls and emails. Six months ago, asked specifically whether federal statutes trumped a president’s war-time authority, McCain said, “I don’t think the president has the right to disobey any law.” Now, McCain has apparently given up on this, and embraced the Bush administration’s “sweeping theories of executive authority.”

Biden, not willing to let opportunities like these pass him by, pounced. (via mcjoan)

…Biden wrote that the FISA statute, which he helped draft, “made clear the exclusive legal steps the President must take in order to conduct national security surveillance.”

“President Bush chose to ignore the law and now it seems Senator McCain will continue this policy,” Biden writes. “Once again – there is no daylight between President Bush and Sen. McCain.”

“We all share the goal of capturing the terrorists and protecting national security and we can do that without violating the privacy of the American people,” he added. “Like President Bush, Sen. McCain is presenting the American people with a false choice — national security or civil liberties. We need a President who understands that we can have both. It’s what our values and our Constitution demands.”

First, good for him. Second, this seems to be part of a trend.

This comes two weeks after Biden went after Joe Lieberman’s latest defense of McCain’s foreign policy worldview…

Last week, John McCain was very clear. He ruled out talking to Iran. He said that Barack Obama was “naïve and inexperienced” for advocating engagement; “What is it he wants to talk about?” he asked.

Well, for a start, Iran’s nuclear program, its support for Shiite militias in Iraq, and its patronage of Hezbollah in Lebanon and Hamas in Gaza.

Beyond bluster, how would Mr. McCain actually deal with these dangers? You either talk, you maintain the status quo, or you go to war. If Mr. McCain has ruled out talking, we’re stuck with an ineffectual policy or military strikes that could quickly spiral out of control.

Sen. Obama is right that the U.S. should be willing to engage Iran on its nuclear program without “preconditions” – i.e. without insisting that Iran first freeze the program, which is the very subject of any negotiations. He has been clear that he would not become personally involved until the necessary preparations had been made and unless he was convinced his engagement would advance our interests.

…which came a week after Biden went after Bush for his “appeasement” talk…

“This is bullshit, this is malarkey. This is outrageous, for the president of the United States to go to a foreign country, to sit in the Knesset … and make this kind of ridiculous statement.”

…which came a few months after Biden made Rudy Giuliani look pretty ridiculous on international current events, back when the former mayor looked like a credible presidential candidate.

I’m not saying Biden’s the ideal running mate. First, Biden led the way on that ridiculous bankruptcy bill, and I’ll probably never forgive him for it. Second, he eschews message discipline, and is well known for sticking his foot in his mouth with embarrassing gaffes.

That said, the more he stays on the offensive against McCain and his cohorts, the more I like him.