U.S. Rep. Ed Markey, of Malden, leads his Democratic rival, U.S. Rep. Stephen Lynch, of South Boston, by 11 percentage points. On the Republican side, former U.S. Attorney Michael Sullivan, of Abington, has the lead over both Norfolk state Rep. Dan Winslow and Cohasset private equity manager Gabriel Gomez.
But so many voters are still undecided that both races are up in the air.
Markey and Lynch are the best-known candidates. Steve Koczela, of the MassINC Polling Group, finds either one would be the candidate to beat in the general election.
"Whether it be Markey or Lynch, they're leading the potential Republican nominees by 17 points or more," Koczela said.
Among voters who said they are more likely to vote in the Democratic primary, Markey leads Lynch 35 percent to 24 percent. But, overall, voters have a more favorable impression of Lynch. He has a 25-point gap between his favorable and unfavorable numbers, compared to Markey, who has only a 9-point gap.
Voters who prefer Lynch and voters who prefer Markey care about some different issues. Voters who like Lynch, for example, care more the about the U.S. military. And it's an issue Lynch has focused on. Last week, he went to an American Legion post in Dorchester to talk about the challenges veterans face.
"Too often, I think, returning veterans from Iraq and Afghanistan and the Gulf War and others suffer in silence," Lynch said.
Voters who like Markey care more about gun control. Markey takes on the National Rifle Association in a TV ad that begins with the famous cry of the group's former president, Charlton Heston: "From my cold, dead hands."
"It's been called the most powerful lobby in America, but that didn't stop Ed Markey," says the ad's narrator.
The greatest number of likely Democratic voters — 41 percent — have yet to make up their minds. So despite Markey's lead over Lynch, the Democratic nomination is up for grabs.
Pollster Koczela finds the same is true on the Republican side.
"There's still a lot of undecided voters out there," Koczela said. "There's a lot who don't really have an image of the candidates."
With more than a month to go to the primary, Sullivan is in the lead among Republicans, with 28 percent of likely GOP voters saying they'd pick him. Winslow is second, with 10 percent, and Gomez trails with 8 percent.
But the big take-home message is that 46 percent of likely voters in the Republican primary have not made up their minds. In part, that's because a large percentage of voters still don't know any of the GOP candidates.
So, like the Democratic nomination, the Republican nomination is also wide open.
The primaries are set for April 30, with the general election on June 25.
The telephone survey of 610 likely voters was conducted last Tuesday through Thursday.
This program aired on March 26, 2013.