His political "coming out" came a year ago, when he delivered a well-received speech to the Massachusetts legislature after the shooting of Congresswoman Gabrielle Giffords in Arizona.
Matt has often been considered the more political-minded of the two; since the two co-chaired Ted's 2006 re-election campaign he has been more active in that realm, working for Barack Obama's presidential campaign in New Hampshire, and working for a stint in the White House.
More than one person I spoke with couldn't help comparing the two to Jack and Bobby, with Joe, like Jack, the charming, affable candidate, and Matt, like Bobby, the savvy operator.
That comparison is not the kind of pressure Democrats want to place on Joe. Insiders expect him to run a low-key campaign of neighborhood hand-shaking appearances, to replace broad Kennedy stereotypes with personal contact.
"He's going to define himself by virtue of running," says political consultant Mary Anne Marsh, of Dewey Square Group. "He's going to travel around that district, and people are either going to like him or not."
He is also going to begin defining the next generation of the Kennedy family — whether he intends to or not. It was Ted himself who, in his surprise appearance at the 2008 Democratic National Convention in Denver, called again for "the torch to be passed again to a new generation of Americans." He meant Obama, but in Massachusetts we will always look to apply it to the Kennedys.
To read the Talking Politics blog, go to thePhoenix.com/talkingpolitics. David S. Bernstein can be reached at firstname.lastname@example.org. Follow him on Twitter @dbernstein.