Al Franken, Getty Images

MINNEAPOLIS (AP) - A new poll shows U.S. Sen. Al Franken with a double-digit lead over Republican challenger Mike McFadden in his campaign for a second term, but the number of likely voters who are undecided is also in the double digits.

The poll for the Minneapolis Star Tribune shows Franken with 49 percent of likely voters compared to 36 percent for McFadden. Eleven percent are undecided.

McFadden has criticized Franken for his steadfast support of President Obama and the Affordable Care Act. Franken's approval ratings of 53 percent are far ahead of Obama's 40 percent in Minnesota. Franken's rating has dropped two percent since February.

The first-term Democrat gets most support from the Twin Cities metro area where two-thirds of likely voters favor him compared to 20 percent for McFadden. In northern Minnesota, 55 percent of those polled support McFadden.