DES MOINES, Iowa — Republicans are struggling to recruit strong Senate candidates in states that present the party’s best opportunities to reclaim the majority, a sign that the GOP’s post-2012 soul-searching may end up creeping into the midterm congressional elections.

It’s admittedly early, with more than 18 months before the November 2014 elections.

But candidate recruitment efforts are well underway. And, so far, Republicans haven’t been able to field a top-tier candidate in Iowa or Michigan, swing-voting states where the GOP hopes to make a play for seats left open by the retirement of veteran Democratic senators. Also, the GOP is facing the prospect of contentious and expensive primary races in Georgia and perhaps West Virginia, two GOP-leaning states where sitting senators -- one Republican, one Democrat -- are retiring.

With President Barack Obama not on the top of the ticket, Republicans may have their best chance in years to try to retake the Senate, which would put a major crimp on the president’s efforts to enact his agenda and shape his legacy in the final two years of his presidency. Republicans need to gain six seats to win control of the Senate. Democrats will be defending 21 seats to Republicans’ 14, meaning the GOP has more opportunity to try to win on Democratic turf.

Only recently, Republicans were reveling in the fact that several veteran Democrats were retiring in states where the GOP had not had a chance to win in decades. Last week, Democrat Max Baucus of Montana became the latest to announce his retirement in a state that typically tilts Republican.

But a combination of no-thank-yous from prospective Republican candidates in Iowa, slow movement among others in Michigan and lack of consensus elsewhere over a single contender have complicated the early goings of what historically would be the GOP’s moment to strike -- the sixth year of a presidency, when the party out of power in the White House usually wins congressional seats.

Despite that historical disadvantage, Democrats are fighting to reclaim the majority in the House, where control will be decided by a couple of dozen swing states.

After embarrassing losses in GOP-leaning Indiana and Missouri last year, the new Republican Senate campaign leadership is responding by wading deep into the early stages of the 2014 races, conducting exhaustive research on would-be candidates, making hard pitches for those they prefer and discouraging those they don’t, to the point of advertising against them. The hope is to limit the number of divisive primaries that only stand to remind voters of their reservations about Republicans.