(CNN) - The 2014 midterm elections may be 18 months away, but congressional campaigns are already gearing up for the fight.
And Republicans hoping to take back the Senate or maintain control of the House may struggle to get their wish, according to a new national poll released Wednesday by Quinnipiac University.
By a narrow margin, American voters say they are more likely to vote Democratic than Republican for congressional candidates, 41% to 37%. The four percentage point difference falls within the poll's sampling error.
The slim Democratic edge has been consistent in Quinnipiac polling for several months, according to Peter A. Brown, assistant director of the Quinnipiac University Polling Institute.
"The question, of course, is whether that margin will be there in 18 months when voters go to the polls," Brown said, adding that almost exactly four years ago, Democrats held a 41%-34% lead in the generic ballot, according to a Quinnipiac survey.
"Eighteen months later, however, Republicans won a historic landslide, picking up 63 House seats," Brown said, referring to 2010 GOP takeover. "Nevertheless, being ahead at this point is certainly bringing smiles to Democratic faces given history."
Why are Democrats slightly ahead? Brown notes that it's not linked to any "strong public affection" for the party. Sixty-seven percent say they disapprove of Republicans in Congress, while only slightly fewer, 60%, feel the same way about Democrats.
The slight edge could be driven by a gender gap where women support Democrats over Republicans, 44% to 35%, while men are slightly more in favor of Republicans, 39% to 38%.
On the issues, voters trust Congressional Democrats more than Republicans on health care, but they say Republicans do a better job handling the budget deficit and gun policies. On the economy and immigration, Republicans and Democrats are more even in the eyes of voters.
When it comes to balance of power on Capitol Hill, 48% of voters say they would like one party to control both houses of Congress and the White House. If Democrats keep control of the Senate and retake the House, such a scenario would be the case during President Obama's last two years in office.
Forty-three percent of voters, however, want to see a more divided government.
The party breakdown in the Senate currently stands at 55 Democrats (including two independents who caucus with the Democratic Party) and 45 Republicans.
Democrats will be defending 21 of the 35 seats up for grabs in November 2014. As of now, six Democrats have announced plans not to seek re-election, including three from right-leaning states. On the Republican side, two senators have said they plan to retire after they finish their term.
In addition to the open races caused by Senate retirements, another high-profile race will come in Kentucky, where incumbent Senate Minority Leader Mitch McConnell will face aggressive Democratic efforts to oust the longtime senator from his seat. While Democrats don't yet have a candidate, McConnell's campaign is already coming out with ads and getting a head-start on the yet-to-be-decided opposition.
On the House side, Democrats would need to make big gains in order to take back the chamber. There are currently 232 Republicans and 201 Democrats, with two vacancies in Illinois and South Carolina.
Quinnipiac surveyed 1,471 registered voters by telephone from April 25-29, with a sampling error of plus or minus 2.6 percentage points.