As you've probably heard, former Secretary of State and Chairman of the Joint Chiefs of Staff Colin Powell, a Republican, endorsed Barack Obama for president yesterday on "Meet the Press." I'm a little late on this--alas, I spent the weekend without my trusty laptop--but I still thought it'd be worthwhile to post a few quick thoughts on what the announcement accomplishes.

Some observers, like the Atlantic's Marc Ambinder, have said that Powell will help Obama overcome any lingering racial opposition. "Powell is a culturally individuated African-American hero," he wrote yesterday. "To the extent that there remain white voters who have inchoate worries about Obama's race, it helps to have him associated with a man whose race they've already gotten over." I disagree. Oprah Winfrey is a "culturally individuated African-American hero," too, but her endorsement of Obama last May hardly gave swing voters a compelling reason to support the Illinois senator. The key thing about Powell isn't that he's black. It's that he (unlike Winfrey) doesn't strike casual voters as your typical Obama supporter. He's a Republican. He's a military man. He backed both Bushes. And he's even donated to McCain. That's why Powell's endorsement is so powerful.

The most important element of Obama's extensive field operation is the local validator: a person who looks like you, talks like you and (presumably) thinks like you but who's still vouching for the unfamiliar face at the top of the ticket. Powell has now become Obama's key validator. Ahead by five to seven points in the polls--often with more than 50 percent of the vote--Obama doesn't need to persuade McCainiacs to jump ship. He simply has to prevent his softest supporters--and a few undecideds--from reverting to his rival. Like Powell, many of these folks are Republicans--some from military communities--who still deeply respect McCain. He's well-qualified to speak to them--and on Sunday, that's exactly what he did.

Powell delivered his argument in two parts. First, he sought to dispel--or preempt--any doubts about Obama. Worried about Obama's inexperience? Don't be, said the general: "he will be ready to take on these challenges on January 21st." he's ready to be president on Day One." Suspect that Obama's tax policies are "socialist"? Nonsense, said the Republican: "there's nothing wrong with examining... who should be paying more or who should be paying less, and for us to say that makes you a socialist is an unfortunate characterization that isn't accurate." Heard that Obama might be Muslim? "He's not," said the familiar, respected figure--but "what if he [wa]s?" "Is there something wrong with being a Muslim in this country?" Powell asked. "The answer is 'no.' That's not America." These are the three issues--experience, taxes and "otherness"--most likely to drive uncommitteds away from Obama on Election Day. Powell was essentially saying, they don't bother me--so they shouldn't bother you.

The pro-Obama part of Powell's endorsement has received the most media attention--and understandably so. But from a political perspective, the other part--the anti-McCain, anti-Republican part--will probably prove more impactful. After praising Obama, Powell questioned McCain's decision to select Sarah Palin as his running mate ('I don't believe she's ready to be president of the United States, which is the job of the vice president"). He criticized McCain's response to the ongoing economic crisis ("almost every day there was a different approach to the problem... he didn't have a complete grasp of the economic problems that we had"). And he denounced the negative tone of McCain's campaign ("what they're trying to connect [Obama] to is some kind of terrorist feelings, and I think that's inappropriate"). Here, Powell echoed the key concerns about McCain among uncommitted voters--Palin, the economy and "politics as usual"--and confessed that he's bothered by the same stuff. Ultimately, it's easier for undecideds to justify siding with Obama--and harder for them to consider reverting to McCain--when someone like Powell, who they tend to trust, respect and agree with, has said he shares their doubts.

Traditionally, endorsements don't sway voters. Powell's won't be any different. Solid Republicans will dismiss it as predictable, or vengeful, or race-based, or whatever. But Powell doesn't have to persuade solid Republicans. He merely has to help Obama hang onto his softest supporters--i.e., maintain the status quo. That lower bar--combined with the right message and the right messenger--could very well make Powell's endorsement the first one in recent memory that actually matters.