WASHINGTON — Senator Kay Hagan, a North Carolina Democrat who is up for re-election, is admonishing Republicans back home as “irresponsible and cold-hearted” for slashing unemployment benefits. Senator Marco Rubio, Republican of Florida, says that her party’s thinking is “stale and old and doesn’t really address the magnitude of the problem.”

Poverty is suddenly the subject of bipartisan embrace.

President Obama will highlight income disparity in his State of the Union address this month, part of a broader effort by Democrats to push a populist theme for their midterm campaigns against Republicans. Republicans are offering solutions that would give the states and the private sector, not the federal government, more authority to help improve the plight of the poor.

Each side’s argument is freighted with difficulty. Democrats could push the rich-versus-poor theme too far, alienating middle-class voters and wealthy donors. Republicans may find themselves painted in the same box as Mitt Romney was in 2012, when many voters saw him as indifferent to the concerns of working Americans.

“A lot of voters felt that President Obama cared more about them than Mitt Romney did,” said Senator Susan Collins, Republican of Maine, who is up for re-election and has proposed overhauling the assistance program for the long-term unemployed by linking benefits to job training. “That was a wake-up call to Republicans that we need a positive approach that gives people reason to believe we want to support policies to create more jobs. And then we can draw the contrasts with the failed policies of this administration.”