With John Kerry officially confirmed as secretary of state, now begins the scramble to fill his Senate seat—and that scramble will include a Democratic primary, between Rep. Ed Markey of Malden and Rep. Stephen Lynch of Boston. And, as Shira Schoenberg reports in today’s Republican, Lynch will officially kick off his campaign in Springfield, with an event at O’Brien’s Corner tomorrow morning at 9.

The Democratic primary will pit the liberal Markey, a member of the Progressive Caucus with a strong record on consumer protections and environmental and energy matters, against the more conservative Lynch, who opposes abortion rights and voted for the war in Iraq. Over his time in office, Lynch has become friendlier to gay rights, softening some of the criticism he once faced from liberal activists. Markey has already sewn up endorsements from some key officials, including Kerry, retired U.S. Rep. Barney Frank, House Speaker Robert DeLeo, Attorney General Martha Coakley and Treasurer Steve Grossman; Lynch, a one-time union head, can expect to enjoy strong support from organized labor.

And at the end of what’s looking to be a fierce party primary in April, whom will the winner face in the June general election? While a few other names have been floated as potential Republican candidates, including former Gov. Bill Weld, most observers expect it to be former Sen. Scott Brown; as the Wall Street Journal recently put it, the “seat is Scott Brown’s for the taking, which probably explains why he’s in no rush to claim it.”

In a recent poll by MassInc. in which respondents were asked about a Brown/Markey match-up, 53 percent supported Brown and 31 percent Markey. Brown’s commanding lead narrowed considerably when respondents were asked if they’d vote for him or an unnamed Democrat, with 44 percent backing Brown and 36 percent a generic Democrat.

Meanwhile, Gov. Deval Patrick is expected to announce today his appointment of an interim senator to fill Kerry’s seat until the June 25 special election.