Mitt Romney has climbed to a commanding 23-point lead over his nearest Republican competitor, with the support of 37% of Republicans nationwide. Rick Santorum and Newt Gingrich each have 14%, and Ron Paul has 12%.

Congress' job approval rating has improved to 25%, the highest since early June.

U.S. population growth has slowed significantly, the result primarily of significant trends related to fertility and immigration.

No third-party candidate gets more than 3% of the vote in the U.S. presidential race, as the vast majority of U.S. voters say they would vote for either Barack Obama or Mitt Romney if the election were held today.

Barack Obama is closely matched against four leading GOP candidates in prospective presidential election trial heats. Mitt Romney edges Obama by two percentage points among registered voters. Rick Perry and Obama are tied, but Obama has a slight ...

Mitt Romney leads Rick Santorum slightly, 34% to 30%, in national Republicans' preferences for their party's nomination. Romney is ahead among most subgroups; Santorum does best among conservatives and in the Midwest.

The Republican presidential race is now a 32% to 30% statistical tie between Mitt Romney and Rick Santorum, in Gallup interviewing conducted wholly after Santorum's victories in the Feb. 7 nominating contests.

Attorney and former Pennsylvania Sen. Rick Santorum is now suffering the fate of former college professor and Congressman Newt Gingrich -- rising to front-runner status among Republicans nationwide and then falling right back down again.

As he turns to the general election campaign, Mitt Romney faces the challenge of generating enthusiasm and, hence, turnout among Midwestern, young, highly religious, and conservative Republicans -- groups among whom he has struggled.

Both leading Republican candidates for president, Rick Santorum and Mitt Romney, are competitive against President Barack Obama when registered voters nationally are asked whom they would support in the November general election.