Informed political observers have realized since June that Hillary Rodham Clinton won’t be Barack Obama’s running mate. As Obama prepares to announce his vice-presidential choice, however, it will be worthwhile to watch the reaction of the ill-informed and unobservant — which is to say, the independent “swing” voters who will ultimately decide the election.

Especially for those swing voters who voted for Hillary in the Democratic primaries, it may come as a brutal shock to learn that the former First Lady won’t be on the ticket in November. The shock will be amplified when those voters learn that Obama’s choice was the result of an ABC (“Anybody But Clinton”) process that excluded Hillary from serious consideration months earlier.

While running mate choices rarely influence the ultimate outcome of elections — Gallup finds only a small “bounce” factor involved in such announcements — this year may prove to be one of those rare occasions.

The potential for a backlash from disgruntled Clinton voters has been consistently derogated by elite political commentators, who climbed aboard the Obama bandwagon early and by March were declaring Hillary’s nomination a mathematical impossibility. Her belated rally in swing states like Ohio and Pennsylvania annoyed these elites, but did not dissuade them from their belief that the Democrats’ downside risk of alienating Clinton voters would be a non-factor in November.

Yet Hillary’s voters were not, for the most part, members of the political elite. She drew key support from blue-collar voters and older women. Already, as a recent Pew Research poll indicates, some 18 percent of those who backed Clinton in the primaries — which translates to more than 3 million voters — are already supporting the Republican candidate, John McCain.

The potential for that number to grow is very real, because many of Clinton’s supporters in the primaries were independent voters who, as American University political scientist Candace Nelson has observed, “are the least likely to pay attention to politics, least likely to be engaged in the political process.”

While Pew found that 72 percent of Clinton’s supporters now back Obama, another 10 percent remain undecided. It is among these independents who voted for Hillary in the Democratic primaries that a backlash could develop when the Democrat names his Anybody But Clinton running mate.

Political obtuseness

Pro-Hillary blogger Big Tent Democrat first pointed to the possibility of such a backlash:

When Obama does not pick Hillary, he will lose support among women and white voters. … His stubborn refusal to pick Hillary Clinton, his insistence in causing political trouble for himself with the VP pick, will make this a closer election than it should be. The political obtuseness on this critical decision is amazing to me.

That prediction was made in late July in reaction to Quinnipiac polls showing the Democrat leading in the swing states of Florida, Ohio and Pennsylvania. At that time, Obama was enjoying a poll “bounce” caused by media enthusiasm for his foreign trip.

Big Tent Democrat didn’t see the damage from an ABC running mate being enough to cost Obama the election, but that was before polls showed a post-Berlin backlash — and before it became apparent that Democrats could be facing unexpected trouble in swing states like Michigan and Pennsylvania.

John Kerry narrowly beat President Bush for Michigan’s 17 electoral votes in 2004, and the state should be considered safe for Democrats in a year when such poll indicators as the generic congressional ballot show Republicans in a slump.

Yet, proving Tip O’Neill’s adage that all politics is local, Michigan Democrats are hurting from reaction to Gov. Jennifer Granholm’s 2007 tax increase and from the scandal surrounding Detroit Mayor Kwame Kilpatrick. Recent polls have shown Obama’s lead as thin as 2 points in the state, and Karl Rove has named Michigan as one of the key “blue” states that McCain might switch to Republican red in November.