The survey suggested that President Obama's current job approval ratings and distrust of the Affordable Care Act are fueling the trend. About 90 percent of respondents said the health care law will be important in their decision of which candidate to vote for, compared to 28 percent who cited immigration reform as an issue.
Politico found 48 percent of those voters say the law should be repealed, 35 percent said it would be changed, and only 16 percent wanted it to stay as is. Obama's job approval rating was 40 percent.
Overall, the poll found 41 percent of voters in swing states and districts said they would vote Republican if the election was held now, compared to 34 percent who said they would vote Democratic. That gives the party a lead of 7 percentage points.
The Democrats have been trying to use issues like pay equity for women, immigration reform, and gun regulations. Politico found that voters even in conservative states are more likely to support the party's position on those issues, but, at least for now, they are not what is driving the election.
The Republican Party, by contrast, has been running against Obama and the ACA.
Charles Pearre, a retired civil engineer in the Washington suburbs in Virginia, said he has not decided who to vote for in this year's election. But Pearre, describing himself as a conservative, said he likes having a split between Congress and the president.
"My opinion of the president is he's not doing a good job at all and he's not qualified," he told Politico. "The health care law, I think, should be totally revised."
The poll of 867 likely voters in areas with close races was carried out by GfK under the administration of SocialSphere Inc.