The crowd at the law office to hear Berwick spilled out into the hallways. The candidate has seemed to gain support from the more progressive in the Democratic party.

PITTSFIELD, Mass. — With the Democratic Convention just two weeks away, gubernatorial candidate Donald Berwick believes he will have the votes to get on the ballot.

Berwick needs 15 percent of delegates to vote his way to be placed on the primary ballot. And with the momentum his campaign has gained recently, he believes he will get it

"I'm sure we are going to be on the ballot. The momentum is stunning. We've had the best fundraising month in our history in May, the number of volunteers has swelled fivefold in two months," Berwick said.

"The response to progressive messaging, for specific bold issues, I can feel it, the momentum is there."

The former administrator of the federal Centers for Medicare and Medicaid Services, where he oversaw implementation of many aspect of the Affordable Care Act, has been gaining support throughout the state from the more progressive Democrats.

Of five potential Democratic candidates, he is the one advocating for a single-payer health care system. Berwick's campaign centers on improving the health care system to pave the way for other progressive issues.

On Sunday, Berwick visited the law office of Sherwood Guernsey, where he met with dozens of progressive Democrats and received support for his vision. Berwick told the crowd that the progressive message is to "show up" to help others of need.

Whether it is helping the homeless, addressing criminal justice reform, to providing more mental health and substance abuse programs, Berwick told those in attendance that he'll talk about and focus on the issues that others have back away from.

"We have a fight on our hands and, with a progressive agenda, we have to assert our values," Berwick said.

Berwick may have hit a niche — especially in the Berkshires where he has campaigned more than most of the Democratic field — with a progressive agenda to get him on the ballot. The next goal would be to win the Democratic primary to be the candidate to take on Republican Charlie Baker.

"Everyone on the Democratic side is very concerned. We have got to keep the corner office in Democratic column. I think I have the best chance at beating Charlie Baker and our momentum is extraordinary," Berwick said.

The campaign, he says, has been built to not only gather delegate support but also is gaining mass attention from the community. The volunteer base has grown to be ready to fully expand the campaign after the election, he said.

Two Democratic candidates entered the race as highly touted elected officials. Treasurer Steven Grossman and Attorney General Martha Coakley are both seeking to replace Gov. Deval Patrick. With most name recognition, they have been the leading candidates in polls.

They could also narrow the number of convention delegates for candidates like Berwick, Juliette Kayyem and Joseph Avellone, to gain their 15 percent.

Even with the two top names expected to be on the ballot, the state Democratic Party has not aligned itself behind a single candidate yet.

In a recent interview, Kayyem, who perhaps has campaigned as much in the Berkshires as Berwick, said the longer it takes for the party as a whole to come to a decision, the better it is for candidates like her.

Kayyem, a former National Security secretary, has been gaining an appeal with the independent voters, so she stands to fare better in a primary than she will at the convention.

She, too, believes she will receive the 15 percent of delegates to be on the primary ballot. Kayyem and Berwick have been running close to each other in polls behind the two leaders.

Avellone, however, has been falling behind and the question leading into the convention is how many Democrats will appear on the ballot.