BOSTON (CBS) – Boston Mayor Tom Menino has finally picked a side in the U.S. Senate race in Massachusetts.

WBZ NewsRadio 1030’s Lana Jones reports

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Sources told WBZ NewsRadio 1030 and WBZ-TV’s Jon Keller Thursday that Menino will endorse Elizabeth Warren at a rally in Roslindale Friday.

Menino has so far refused to say who he’d support.

The mayor, who’s a Democrat, has been friends with Republican Senator Scott Brown for years.

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Menino endorsed Martha Coakley in Brown’s last race, but Keller said that support was lukewarm.

“There was clearly not much juice behind that and that matters.  A Democratic candidate running statewide has got to come roaring out of Boston with a huge vote advantage in order to propel them statewide,” Keller said.

Brown and Warren will face each other in their first debate tonight on WBZ-TV at 7 p.m.

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You can also watch it live on CBS and listen live on WBZ NewsRadio 1030.