For months, representatives of the left wing of the Democratic Party have been urging U.S. Rep. Richie Neal to move a bit in their direction. Recently, their nudging paid off—thanks, in good part, to a looming September party primary.

Earlier this month, the Progressive Democrats of America announced that Neal has agreed to sign on as a co-sponsor of a package of bills backed by the group. They include universal healthcare proposals, job creation bills and a call for the withdrawal of troops and defense contractors from Afghanistan. Also on the list: a proposed constitutional amendment filed by Rep. Jim McGovern of Massachusetts’ 3rd District (for the time being, anyway) that would overturn the Supreme Court’s controversial Citizens United decision by making clear that corporations do not have the same rights as individuals.

PDA members and fellow activists have been holding regular lunchtime vigils outside Neal’s office in Springfield’s federal building since late 2010, calling on him to back the bills. (The group has also targeted other Democratic legislators, holding similar vigils at their offices.) Recently, PDA was granted a meeting with Neal, and he agreed to come on board.

What persuaded the Congressman to come around? Could it have anything to do with the fact that this fall he’ll face two challengers in the Democratic primary, both of them self-described progressives who’ve taken every opportunity to cast Neal as the big-money, insiders’-club candidate?

Those challengers—Bill Shein, a writer from the Berkshires, and Andrea Nuciforo, a former Pittsfield state senator—will compete with Neal to be the Democratic nominee for Massachusetts’ newly created 1st Congressional District. That district comprises Berkshire and Hampden counties, large parts of Franklin and Hampshire counties, and a portion of Worcester County. (Some Valley communities previously represented by Neal, including Northampton, will shift into a new 2nd District, where McGovern, a member of PDA’s Advisory Board, is the incumbent.)

Neal’s opponents were quick to weigh in on his change of heart. “If a primary challenge forces him to vote like a Democrat, then we applaud the congressman for making the right decision,” James Pollock, a Nuciforo spokesman, told the Daily Hampshire Gazette.

Shein was even more pointed: “Where has he been all these years? It’s hilarious and embarrassing to see someone pander so transparently in an election year. The last thing we need is more election-year followers.”

While PDA, in its announcement, acknowledged the role Neal’s primary competition likely played in swaying him to its side, the group also reminded supporters that their continued pressure on Neal helped, too, saying, “We all know … if we had not been consistently working to put him on record, none of this would have happened.”