Incumbent Democrats Gov. Mark Dayton and Sen. Al Franken both lead all their potential Republican opponents in a new poll.

Public Policy Polling released the poll Tuesday. It showed Dayton and Franken with leads of 10 points or more above the respective fields of GOP candidates vying to challenge them in November. In both races, the Republican challenger won't be set until an August 12 primary election.

In the U.S. Senate race, Franken leads Republican businessman Mike McFadden, 49 percent to 38 percent. McFadden is the GOP's endorsed candidate in the race and seen as heavy favorite in the August primary.

Franken, running for his second term, holds similar leads over the other Republicans on the primary ballot: Jim Abeler (50 to 39), David Carlson (49 to 38), Patrick Munro (50 to 35) and Ole Savior (50 to 33).

Dayton holds similar leads over his possible GOP rivals, though his support tops out slightly lower than that of Franken. In five possible matchups, Dayton is at 47 percent in all of them. Of the Republican candidates, Scott Honour is at 35 percent, Jeff Johnson at 36 percent, Marty Seifert at 36 percent, Kurt Zellers at 37 percent and Merrill Anderson at 35 percent.

Johnson is the endorsed GOP candidate, but none of the candidates has emerged as a clear frontrunner in the Republican primary.

The poll found most voters still know little about the Republican candidates in either race. In the Senate race, 71 percent of respondents said they were "not sure" when asked if they had a favorable or unfavorable opinion of McFadden. That margin was even higher for the other GOP Senate candidates.

The poll showed the party's candidates for governor are similarly not well known, with between 61 percent and 80 percent of respondents holding no opinion of them.

There's much less gray area in voters' opinions of Franken and Dayton. Franken, elected by a razor-thin margin in 2008, has a 50 percent approval rating and a 40 percent disapproval rating. Dayton, who also won a close race in 2010, gets a 48 percent approval rating and a 41 percent disapproval.

President Barack Obama got a 44 percent approval rating in the poll, with 50 percent disapproving. The state's other DFL senator, Amy Klobuchar, got a 56 percent approval rating with 32 percent disapproving.

Public Policy Polling surveyed 633 registered voters in Minnesota from June 12-15. The poll's margin of error is plus or minus 3.9 percent.