Monday, Sen. Tim Johnson (S.D.) became the latest Democrat to announce his retirement from a state where Republicans have a good shot at picking up a seat in 2014. Already Sens. Tom Harkin (Iowa), Frank Lautenberg (N.J.), Carl Levin (Mich.) and Jay Rockefeller (W.Va.) have announced their intent to retire next year. Meanwhile, Sens. Mark Pryor (Ark.), Mary Landrieu (La.), Mark Begich (Alaska), Kay Hagan (N.C.) and, perhaps, Mark Udall (Colo.) are vulnerable, given their super-liberal voting records in purple or red states.

Sen. Mitch McConnell-Andrew Harrer/Bloomberg Sen. Mitch McConnell-Andrew Harrer/Bloomberg

On the GOP side, Sen. Susan Collins (R-Maine) announced that she will run for reelection. Two Republican retirees, Sens. Saxby Chambliss (Ga.) and Mike Johanns (Neb.), will leave with undistinguished terms, but they hail from red states that are not likely to flip over.

Republicans certainly have managed to blow opportunities like this before with rotten candidate selection. It isn’t clear that the Republican primary electorate has figured out the keys to winning open or weakly defended Senate seats.

For starters, provided they don’t veer into Todd Akin territory with maladroit or downright stupid comments, not every state is so deep red that the grass-roots can afford to go for full-throated conservatives. The GOP need not worry about finding a centrist in Georgia, for example. However, Pryor, Landrieu,  Begich, Hagan and Johnson got to the Senate by riding on the turnout wave in President Obama’s first election and by persuading Republicans and independents they were moderates. The GOP contenders for those states will have to argue that the incumbents were phony moderates who rubber-stamped the entire agenda. But it would be a mistake to assume this is all they have to do. These states, along with South Dakota and West Virginia, have shown themselves averse to voting by party line. In these races, the balance is held by quintessential swing and ticket-splitting voters; a Georgia-style Republican may run poorly in, say, West Virginia.

The Republican candidates in gettable states have to be not simply good attackers but also appealing figures who can be effective in getting Democrats and independents to vote for them. In part, they will have to make the case that a GOP-controlled Senate and the demotion of Senate Majority Leader Harry Reid (D-Nev.) will in and of itself be a service to the country. That entails setting forth positions and agenda items on which, without a Democratic Senate majority, there could be real progress. Energy development, education reform and modification or repeal of the most disagreeable parts of Obamacare (e.g. the medical-device tax) should be on the list. If immigration doesn’t get done before the election, common-sense immigration reform with border security becomes another policy plank for GOP contenders.

Most important, however, is finding quality candidates. This doesn’t refer simply to those who are ideologically compatible with the states in which they are running. It means no more tired retreads (e.g. Tommy Thompson, George Allen), unpolished outsiders, intemperate extremists (e.g. Sharron Angle) or plain-old wackos (e.g. Christine O’Donnell). All candidates should get a thorough vetting and be required to show their mettle in debates and interviews.

If the GOP repeats the errors of 2008, 2010 and 2012, I suppose one can conclude that its voters are unteachable. Permanent minority status in the Senate may well be the result. But if, whatever their ideological disposition, GOP voters find candidates who match up well with their respective states and don’t blow themselves up, then the Senate majority is within the GOP’s grasp.