Longtime Virginia Republican Senator John Warner announced his endorsement of incumbent Democrat Mark Warner Monday

John Warner was a mainstay of the Virginia GOP for decades. A relatively moderate Republican, he served 30 years in the U.S. Senate from 1978 to 2008. The aristocratic Warner, who was married at different times to both a Mellon heiress and Elizabeth Taylor with the epitome of traditional establishment Republican. His endorsement of Mark Warner is a major boost to the centrist Democrat who is up for re-election to his second term in the U.S. Senate in 2014. Mark Warner is a former Governor of Virginia who also unsuccessfully ran for Senate against John Warner in 1996.

This endorsement comes shortly after longtime Republican insider Ed Gillespie entered the Senate race and signals a major shift in the race. Gillespie, a lobbyist, political consultant and former George W. Bush White House aide who served as chair of the RNC from 2003-2005. His entry into the race was supposed to provide Mark Warner a credible opponent in this swing state as well as unite the deeply divided Virginia GOP, where social conservatives and Tea Partiers have long been feuding with the party establishment.

This rift came to the fore during the state's 2013 gubernatorial campaign when social conservative Ken Cuccinelli lost to Democratic fundraiser Terry McAuliffe while suffering a number of notable Republican defections. In particular, Cuccinelli's top rival for the GOP nomination, Lt. Gov. Bill Bolling refused to endorse in the race and one of his key advisors, Boyd Marcus, openly backed McAuliffe.

John Warner's endorsement is not a gamechanger, few, if any, endorsements actually are. But, it's the first time that he has ever openly backed a Democrat and marks an important indicator of changing political currents in the Old Dominion. With Virginia emerging as a key swing state nationally, it marks a bad omen for Republican fortunes in 2016 who need to win back the independent voters and centrists who long supported John Warner throughout his political career.