In the world of political endorsements, the president's is the gold standard… but President Obama has lost a lot of luster.
He arrives here with his popularity nationwide underwater. Add up all the polls, and more Americans disapprove than approve of the way he's doing his job.
Yes, he's more popular in Massachusetts than in many other states, but a poll this week showed his job performance and favorability numbers dropping here, too.
Still, a presidential endorsement has undeniable value. If nothing else, it will help Ed Markey dominate campaign coverage for a day, and it will be a signal to undecided voters that Obama wants him in Washington.
On the negative side, it will reinforce Gabriel Gomez's arguments that he's running against a Democratic machine, and that the party is worried about Markey losing.
Obama has been a regular at election time here, campaigning for Elizabeth Warren last year, helping her win.
His endorsement of Martha Coakley in 2010, didn't help her at all.
He's also come twice to support his friend, Governor Deval Patrick, once for re-election and once in 2006, when Patrick was running for the first time and Obama was still a U.S. senator from Illinois.
So President Obama is three for four in supporting winners here, and Markey is hoping he'll make it four out of five.
But make no mistake, the president is here not only for Markey, but for himself as well.
Obama said, "I need Ed Markey in the United States Senate."
The truth is, the president may need Ed Markey more than Markey needs him.
Because if Markey loses the senate race, he'll stay in the US House. But Obama will lose a dependable senate vote for virtually everything he wants.