Maria Cantwell isn’t up for re-election, but you wouldn’t know it by watching her. She’s been hitting the streets, shaking hands, building support. The Democratic senator from Washington state is campaigning hard for a 50% expansion and other key reforms to the low-income housing tax credit (LIHTC) program.

She announced the effort at a Seattle affordable housing development in March, promising that the effort wouldn’t end there. Sure enough, in April, Cantwell again called for a housing credit increase, this time in New York with Sen. Chuck Schumer (D-N.Y.). Her crusade continued into May, when she was back discussing affordable housing in Walla Walla in her home state.

At a time when rents are rising beyond the reach of many families, her proposal would create or preserve approximately 400,000 additional affordable housing units over the next decade. Those units can’t get built fast enough. There are 11.2 million extremely low-income renters and just 7.3 million affordable units, a big shortfall of 3.9 million. Not counting those places that are structurally inadequate or occupied by higher-income households, there are just 34 affordable units for every 100 extremely low-income renters, according to Harvard’s Joint Center for Housing Studies.

Cantwell has been building a case for the LIHTC program before introducing the legislation needed to make her desired changes. A bill had yet to surface at press time, in mid-May. When it does, no one should have any illusions that it will be easy to pass, even with the credit’s history of bipartisan support.

As much as Cantwell tries, she won’t be able to make changes on her own. Through her website, the senator is asking people to share their stories about homelessness and affordable housing. You can also join and follow the A.C.T.I.O.N. Campaign, a coalition calling on Congress to expand the LIHTC program.

It’s often said that change starts first in the streets, and that’s where Cantwell will win this fight.