Voters are going to the polls in five U.S. states to determine candidates for the mid-term elections in November.
Republican Senators John McCain and Lisa Murkowski are facing challenges from candidates supported by the conservative Tea Party movement.
McCain is expected to easily defeat former U.S. Representative J.D. Hayworth in the Arizona contest. Recent public opinion polls indicate that McCain, a veteran lawmaker and his party's 2008 presidential candidate, holds a double-digit lead over his challenger.
McCain has spent $20 million on the campaign, compared to about $3 million for Hayworth.
In Alaska, Senator Murkowski is facing a challenge from Joe Miller, who is has been endorsed by former Governor Sarah Palin.
In Florida, voters will choose a Democratic candidate for the U.S. Senate. U.S. Representative Kendrick Meek is facing billionaire real estate investor Jeff Greene, who spent millions of his own money on the race.
The winner in the Florida Senate primary will face Republican candidate Marco Rubio and current Governor Charlie Crist, who is running as an independent.
Florida and Alaska also are holding Republican primaries for governor.
In Vermont, five Democrats are vying for the chance to become the party's nominee for governor. The winner of that race will face off against Republican Lieutenant Governor Brian Dubie in November.
In Oklahoma, two U.S. House Republican nominations will be decided in a run-off from an earlier primary.
The entire House of Representatives and one-third of the U.S. Senate are up for election in November. The general election is considered to be a referendum on U.S. President Barack Obama's first two years in office.
President Obama wants to do all he can to limit Democratic losses this year, well aware that an erosion of the Democratic majorities in the House and Senate will have enormous political implications for his ability to govern over the next two years.
Some information for this report was provided by AP.