SEATTLE — A group of political independents that includes Alaska Gov. Bill Walker has endorsed a candidate for the Washington state Legislature, part of a plan to mount a national challenge to the two-party system at this year’s midterm elections.

Unite America, formerly known as the Centrist Project, said it has raised $3 million to help re-elect Walker and fund gubernatorial candidates in Maine and Kansas, Senate candidates in Missouri and Maryland, in addition to state legislative hopefuls in Colorado and Washington. That’s 10 times more money than the group was able to raise in the last election cycle.

“Millions of Americans feel politically homeless as both parties have moved to their extremes,” Nick Troiano, executive director of United America, said Thursday in an interview in Seattle. “That has created a marketing opportunity for political movements like ours.”

Challengers to historical dominance of Republicans and Democrats hope to find renewed opportunity to win voters amid growing polarization. A Gallup poll in January showed 44 percent of Americans identify as independents, compared with 35 percent a decade earlier. Unite America says its goal is to win enough seats in closely divided bodies to control the balance of power, rather than establish a traditional political party.

“There’s increasing space for a new coalition from the center left to the center right,” Bill Galston, senior fellow at Washington D.C.-based Brookings Institution, said in a phone interview. “If you imagine that the Republican Party ticket in 2020 is headed by Donald Trump and Democratic ticket is headed by Bernie Sanders, I would predict that there would be a well-financed third party ticket. That would be the greatest opportunity in two generations to change the basic structure of American party politics.”

In Washington, Unite America is working with Washington Independents to back Ann Diamond’s run for the District 12 seat in the House. She said she’s running as an independent because in her rural part of north central Washington people have grown “frustrated” with the political system, especially after this year’s capital budget cut out funding for services such as a local clinic, roads and fire house restoration.

Chris Vance, co-chair of Washington Independents said his group’s aim is to back a “strong” candidate for the governorship in 2020. Vance is a former legislator who once headed the state’s Republican Party before leaving it last year.

Unlike existing parties, Unite America representatives said they don’t have fixed positions on any of the issues that traditionally group voters in categories.

“We believe in a process that allows input from all sides of an issue; we may not all agree on the same thing,” Walker said. “What may be good for my state may not be good for Kansas or Maryland. You can be who you are and still participate in the process, whereas with the partisan situation you have to take the party line and not deviate from that.”