Ideally, a sponsor interested in organizing a meaningful debate would like to limit it to, say, the six top-tier candidates.

As it happened, however, the Republican Party had difficulty in drawing top-tier candidates to any of the three races.

Mr Gingrich is revelling in his new status as one of two top-tier candidates.

His entry on August 14, 2011, garnered tremendous publicity and made him an instant top-tier candidate.

This election was the last before a flood of potential top-tier candidates was set to enter the ballot in the coming years:

Republicans had trouble recruiting a top-tier candidate.

"I'm not going to be competitive in that area with the top-tier candidates," Mr. Richardson said.

Howard Dean announced yesterday that he had raised close to $9 million this year, establishing himself as a top-tier candidate in the Democratic presidential field.

Party strategists say their top-tier candidates will have the financial resources they need, with both parties planning significant advertising in crucial states.

These polls only showed the results of the top-tier candidates who were viable to win the caucuses.