Once, in the time before super PACs and independent expenditures, before blogs and social media made even local elections a national sport, great herds of split-ticket voters roamed the plains. They voted easily for a Democrat for one office, a Republican for the next, with little consideration for future political scientists who would puzzle over their motives. But now, ravaged by decades of hyper-partisanship, the split-ticket voter is becoming an endangered species.

For generations, voters handed presidential electors to one party and Senate seats to the other. In 1992, as Bill Clinton won New York, Pennsylvania, and Oregon, Republican Sens. Alphonse D’Amato, Arlen Specter, and Bob Packwood won reelection. George H.W. Bush won North Dakota, South Dakota, and South Carolina, even as Democratic Sens. Byron Dorgan, Tom Daschle, and Fritz Hollings won their races.

But in recent years, the number of senators who represent states that vote the other way in presidential elections has decreased dramatically. In 2008, only five senators, all Democrats, won races in states that voted for the other party’s presidential candidate. Only 12 Republican senators hail from the 28 states President Obama won in 2008; only nine Democrats represent the 22 states John McCain won that year.

The correlation between presidential votes—and even presidential approval ratings—and Senate winners is growing stronger. And that could be a daunting prospect for Democrats’ hopes of keeping control of the upper chamber this November.

Several Democrats will face voters in states the eventual Republican presidential nominee will likely carry. Sens. Claire McCaskill, D-Mo., and Jon Tester, D-Mont., represent states Obama’s campaign has signaled they will not seriously target. Seats held by retiring Sens. Kent Conrad, D-N.D., and Ben Nelson, D-Neb., are the likeliest to fall into Republican hands. Democrats will also defend the seat of Sen. Bill Nelson, D-Fla., and those held by retiring Sens. Jim Webb, D-Va., and Herb Kohl, D-Wis., in presidential battleground states.

Even in states where both Senate candidates have millions of dollars to define themselves as independent voices in Washington, recent elections suggest fewer voters are actually making the distinction between, say, a Missouri Democrat and a national Democrat.

In 2006, President George W. Bush’s approval rating was underwater in the six states where Democrats won Republican-held Senate seats. And in all but one of those cases, at least 82 percent of voters who disapproved of Bush’s job performance chose the Democratic candidate, while at least 81 percent of those who approved of Bush voted for the Republican.

The lone exception to the rule still demonstrates just how big an impact a president’s approval rating can have on a race. In 2006, then-Sen. Lincoln Chafee, R-R.I., enjoyed sky-high approval ratings. On Election Day, 63 percent of voters told exit pollsters they approved of the job Chafee was doing. But that wasn’t enough; Democrat Sheldon Whitehouse took 54 percent of the vote and won the seat. Bush’s terrible image in liberal Rhode Island played a huge role: Three-quarters of the electorate disapproved of his job performance, and two-thirds of those voters backed Whitehouse over Chafee—enough to give the Democrat a majority even before factoring in pro-Bush voters.

Obama’s approval ratings are far better than Bush’s were in 2006, but they remain below 50 percent. In some states, his popularity will work in Democrats’ favor: Sen. Scott Brown, R-Mass., will have to win over a significant portion of voters who approve of Obama’s job performance. And though the eventual winner of Hawaii’s late, and possibly ugly, Democratic primary will face off against well-funded former Gov. Linda Lingle, Obama’s win percentage in the Aloha State will be so overwhelming as to give that Democratic Senate candidate a big advantage.

In states like Missouri and Montana, though, both of which Obama lost in 2008, the president could prove more of a drag on the ticket than a boost. A collection of Gallup interviews throughout 2011 showed his approval ratings in both states were lower than his average approval rating across the country; those interviews showed Obama’s approval rating nationally stood at 44 percent, while it was just 39 percent in Missouri and a dismal 34 percent in Montana.

Democrats who have seen the party’s internal polling say their candidates are running well ahead of Obama in both Missouri and Montana. And, they say, neither race will become a referendum on the president.

But Republicans are confident in their numbers as well. A Public Opinion Strategies poll, conducted for Republican super PAC American Crossroads, showed Tester outperforming Obama by 6 percentage points—but trailing Rep. Denny Rehberg, his Republican opponent, by 11 points. Even if that survey, conducted Jan. 9-10 among 400 likely voters, skews too heavily toward Republicans, as Democrats allege, the fact that Obama’s numbers are so weak there is sure to hurt Tester. A private poll conducted for Republicans in Missouri on Jan. 16-17 showed the president’s approval rating at 44 percent, scary territory for a Democrat sharing the ballot with him.

Tester, McCaskill, and other Democrats will have millions in advertising to bolster their reelection bids. And if the economy continues to improve, Obama’s numbers will rise nationally. But in red states, Democrats may find that the elusive split-ticket voter is going the way of the dodo, and to their detriment.

This article appeared in the Thursday, February 2, 2012 edition of National Journal Daily.

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