Farm Belt and Southern voters who prefer a Republican president but have often backed moderate Democrats for Congress seem increasingly inclined to vote GOP in all federal races.
Republicans rejoiced at Conrad's announcement Tuesday. They're convinced that they can win the open seat in 2012 and hold it for years to come. They see it as a replay of last fall's election in the state, when Republican John Hoeven easily won the seat held by 18 years by Democrat Byron Dorgan.
They also point to neighboring South Dakota. After Republican John Thune narrowly defeated Democratic Sen. Tom Daschle in 2004, Democrats didn't even bother last year to oppose Thune's re-election. Republicans feel they can hold the seat for many years, and they are eyeing the state's other seat: Democrat Tim Johnson is up for re-election in 2014.
Democrats say the GOP celebration is premature. They hope to find a strong candidate to run for Conrad's seat. They also say 2012 may be a much tougher year for Republicans than was 2010, especially if President Barack Obama regains his former popularity and Republicans nominate a flawed challenger.
Republicans see several Southern and border states as harbingers of where they hope the Dakotas are heading, with long-term implications for U.S. In the mid-1990s, there were Democratic senators from Alabama, South Carolina, Tennessee, Kentucky, Texas and Oklahoma. Both Georgia senators were Democrats 10 years ago. Now, all those states' senators are Republicans, and they rarely break a sweat when seeking re-election.
The same is true in Wyoming, Idaho, Utah and Kansas.
Like the Dakotas, those states are so solidly Republican at the presidential level that Democratic nominees mostly ignore them. Some Republicans believe that every time a veteran Democrat such as Conrad, Dorgan or Daschle leaves office, there's a good chance the GOP can make a long-term claim to the seat, as they have in much of the South and Mountain West.
"The Dakotas are long gone in terms of states that Democrats can expect to win," said Republican strategist Brian Nick. He noted that the only House members representing the two states -- Democrats Stephanie Herseth Sandlin of South Dakota and Earl Pomeroy of North Dakota -- were ousted by Republicans last fall.
Democrats say they may fare well next year in North Dakota and elsewhere, in large part because Republicans might continue to damage themselves with tea party-dominated primaries. Such primaries last fall nominated unconventional Senate candidates who lost in Delaware, Nevada, Colorado and other states where the GOP had hoped for wins.
"Republican primaries cost them Senate seats last cycle, and there's no question it could happen again," said Democratic spokesman Eric Schultz. "It's far too early for Republicans to declare any victories."
Conrad's retirement is more likely to change the Senate's partisan makeup than is Connecticut Sen. Joe Lieberman's decision to leave. Lieberman is an independent who mostly votes with Democrats, and Democrats will be favored to hold his seat.
If Republicans are right about the Dakotas trending their way, it could boost their hopes of controlling the Senate in future years. Democrats hold the Senate majority thanks largely to Senate victories in states carried by Republicans in the last three presidential elections. They include Montana, West Virginia, Arkansas, Louisiana, Nebraska, Missouri and the Dakotas.
Democrat Blanche Lincoln lost her Senate seat last fall in Arkansas, which voted overwhelmingly against Obama in 2008. Now Republicans are focusing their 2012 efforts on Democratic senators from other states that Obama lost: Ben Nelson of Nebraska, Jon Tester of Montana, Claire McCaskill of Missouri and Joe Manchin of West Virginia. Manchin won a special election last fall and now will seek a full six-year term.
Of course, Republicans must defend some Senate seats in states that Obama won. Sens. Scott Brown of Massachusetts and John Ensign of Nevada may be especially vulnerable. Elsewhere, GOP Sens. Richard Lugar of Indiana and Olympia Snowe of Maine could face tea party challenges in their primaries.
Republicans feel the national trends, on balance, favor them.
"The alignment of states' presidential votes with representation in Congress has been taking place for almost two decades," said GOP consultant Terry Nelson.
Popular and skilled politicians will still be able to win in adverse environments, he said, pointing to Manchin's West Virginia win. But in states like the Dakotas, Nelson said, it will take a special Democrat to overcome the GOP tilt.
Political scientists caution against broad predictions. "Election patterns of the United States are perpetually in flux," said Duke University's David Rohde.
The most dramatic change of the past few decades was the realignment in which the South and the Northeast swapped places to become Republican and Democratic bastions, respectively. The shift has driven many moderates from both parties, a trend that worried Conrad, Dorgan and others as their re-election campaigns neared.
Bill Schneider, a pollster with the Democratic group Third Way, said it's entirely possible, but not certain, that states such as the Dakotas, Nebraska and Louisiana will become reliably Republican in Senate elections as well as presidential contests.
Voters will continue to elect governors and even U.S. House members in ways that defy easy predictions, he said. But at the top of the ballot, Schneider said, "there's been a slow regional realignment to one party or the other." The chief impact, he said, is on Senate races.