For many decades, political scientists have pondered the question: What effect does

For many decades, political scientists have pondered the question: What effect does a political endorsement have on propelling a candidate to victory? And the answer: A little, perhaps a point or two in the polls at most, but not much more than getting a newspaper’s stamp of approval, which is to say, that and dime will get you a cup of coffee.

When Dwight Eisenhower finally (and reluctantly) threw up his support to Richard Nixon in his 1960 race against John Kennedy it was widely thought that Tricky Dick would squeak out the win. He didn’t. Eight years later, Hubert Humphrey made certain to keep his distance from the highly unpopular Lyndon Johnson. Again, that didn’t help the Happy Warrior anymore than Ike’s tip of the hat.

None of this, of course, diminishes its importance, and besides, any candidate would rather have them than not. So this is a good day for state Sen. Ed Murray who today received an endorsement from ex-Governor Chris Gregoire. She joins former three-term Seattle Mayor Charley Royer, who gave his nod of approval to Murray on Friday. Royer was an early supporter of Councilman Tim Burgess, who made a sudden, surprising exit from the race last Friday.

“Throughout his career, Ed Murray has successfully taken on the tough issues, and he’s succeeded by building coalitions no one believed were possible. I’ve seen him do it on transportation, on budgets, and of course on civil rights and marriage equality,” Gregoire said in a statement. “I believe Seattle would benefit from that kind of collaborative leadership, and I am happy to offer Ed my enthusiastic support.”

Said Murray: “I am honored to have the support of two our state’s most respected citizens. They know me and know what I have accomplished, and they know what it takes to govern successfully, so to earn their support for my bid for Seattle mayor is both an important vote of confidence and a great indication of the building momentum behind this campaign.”

It’s difficult to measure the worth of Gregorie’s endorsement. In her final year in office, in 2012, Gregoire — who you may recall, came late to the full marriage rights for gays party (a signature accomplishment for Murray)– her approval rating languished at between 37 and 42 percent. So whether or not she’ll lend any firepower to Murray’s candidacy remains to be seen. It might even backfire and fortify a growing impression that Murray is more a creature of Olympia than the city he wants to lead.

The latest mayoral poll from King 5 News shows Murray with 15 percent, trailing incumbent Mayor Mike McGinn, with 22 percent and former councilman Peter Steinbrueck with 17 percent.