Senator Mark Begich of Alaska is embroiled in one of the toughest reelection fights in the country. His solution, in part: To campaign on a proposal that’s far outside the mainstream of what appears to constitute respectable Beltway discourse on entitlements.

That would be the idea of expanding Social Security benefits, rather than cutting them.

Senator Begich is one of a small but growing group of Democratic lawmakers who support the idea of lifting or changing the payroll tax cap, so higher earners pay more, while adopting a new measure for inflation that would increase benefits for all seniors. This is in contrast to the “Chained CPI” proposal that would use an index leading to a benefits cut, which Obama has championed. The idea behind expanding benefits is that large percentages of seniors’ income goes to costs that have risen faster than inflation, like medical care and housing.

Dems have been perhaps overly willing to get drawn on to GOP austerity turf by debating spending cuts. But Begich makes a startling suggestion: Talking about expanding Social Security benefits is good politics for Dems.

“When you tell seniors, `We want to make sure your dollars rise as your costs do,’ there is automatic excitement because they recognize we understand what they’re going through,” Begich told me today. “Are we for or against helping seniors have a dignified life in their later years? I’m for that.”

Begich noted that the Republicans vying in a primary to face him either support Chained CPI, or voted for the Ryan budget to cut entitlements, or were backed by outside groups that want to cut Social Security. He added that calling for expanding benefits would sharpen the contrast with them: “They would reduce the benefits of seniors. I’m working to make sure benefits are preserved and increased to reflect the costs seniors face.”

Begich added that he’d campaign on the issue, and pointed to a strong local angle. “One in nine Alaskans receives Social Security in one form or another,” he said. “This is good politics and policy. It puts fairness back into the cost of living adjustments. It says to seniors, `We recognize adjustments do not recognize the cost increases that you have had.’ I will talk about it a lot.”

Begich will need good issues. After all, he’s campaigning for reelection in a red state and the prognosticators say his race is a true toss-up. Asked to respond, he admitted he’d like to see more Dem pushback against ads from the Koch-backed Americans for Prosperity but insisted he’d prevail.

“This will be a tough race until the end of the day,” he said. “The third party groups are starting to spend very heavily. It would be nice to have any group pushing against them.”

Progressives groups pushing this proposal argue that campaigning on strengthening and expanding social insurance programs — at a time when stagnating wages and the lingering damage of the Great Recession have increased anxieties about financially unsustainable retirement – would be the best way to remind voters of traditional Democratic Party strengths even amid a tough environment. Given the closeness of the Alaska Senate race, this may be the best test case we get of how expanding Social Security plays on very difficult political turf.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.