The Alabama and Mississippi primaries, along with the Hawaii caucuses on Tuesday, pushed the Republican presidential contest beyond the halfway mark. Voters in 27 states have now weighed in on the process of selecting delegates for the party’s nominating convention, but have brought only limited clarity to the race.

While voters in the two Southern states were closely divided on their preferred Republican presidential candidate, they found more agreement on the top quality they were looking for: the ability to defeat President Obama. In both states, exit polls found, Mr. Romney had a strong electability edge, but it was not enough to overcome concerns that he was not sufficiently conservative.

While Mr. Romney still holds many advantages over his rivals as the race moves to the Missouri caucuses on Saturday and the Illinois primary next week, his aides acknowledge that he is unlikely to reach the 1,144 delegates needed to secure the nomination for at least two more months. His challengers have gradually given up on the idea of surpassing him and have turned to a strategy of trying to block him from reaching the delegates he needs before the convention.

While he played down his defeats on Tuesday night, Mr. Romney had campaigned aggressively in Mississippi and Alabama in pursuit of the combined 90 delegates at stake, but also to demonstrate that he could appeal to Republicans in Southern states, the party’s base. He struggled to make that appeal to a majority of the party’s primary electorate.

The race here, as in other parts of the country, often seemed as though it revolved largely around Mr. Romney. His leading rivals repeatedly criticized him — his record as governor of Massachusetts and his evolving views on social issues provided chief targets — in hopes of planting doubts about his candidacy and improving their own standing with voters.