A renewed wave of political ads are adding heat to Minnesota's sultry summer television viewing.

With one of the nation's most expensive U.S. Senate races on the air, gubernatorial candidates making their cases and outside groups adding volume, paid political pitches are redoubling their assault.

The candidates and their friends have already spent at least $3 million to air their messages across the state and groups are reserving even more time for later in the year.

In recent weeks, the paid advertising messages came into sharper focus.

On Monday, Republican U.S. Senate candidate Mike McFadden announced he would broadcast an ad called "Stitches," in which he and his son brag that McFadden took his sons sutures out himself rather than paying medical professions to do it. The ad, which had a limited cable run earlier this year, came on the heels of an ad in which McFadden was hit below the belt by a kid he was coaching in football.

While those ads have begun to get significant notice, Democratic U.S. Sen. Al Franken's ad budget far surpasses what McFadden has spent. Franken has ponied up more than $1.5 million to spread a message that he cares more about regular Minnesotans than partisan Washington fights.

Franken has more money to spend. He is one of the Senate's most prodigious fundraisers and raised more than all but one incumbent in the last quarter of the year, according to recent reports.

While that premiere race has yet to attract much outside cash in recent months, races lower on the ballot are attracting notice.

Republican gubernatorial candidate Jeff Johnson supporters banded together to produce an advertisement designed to support the party-endorsed candidate. Group volunteer Chris Tiedeman, an RNC committeeman, told Politics.MN it would air on television in the coming weeks.

Johnson's campaign said on Monday it would start running its own ads on cable in advance of the primary. Like McFadden's "Stitches" ad, the Johnson ad has been online for months and, like the McFadden ad, it take a lighthearted approach to a serious issue.

Republican Rep. Kurt Zellers, who will vie against Johnson, former Rep. Marty Seifert and businessman Scott Honour, started his own paid advertising program last week. Honour's consultant Pat Shortridge said Honour has spent almost $100,000 on cable ad time and another $42,000 on radio ads. A group largely funded by Honour's former employer, the Gores Group, has also spent more than $200,000 to support Honour.

Meanwhile, the man the Republicans hope to unseat, DFL Gov. Mark Dayton has yet to storm the airwaves -- but his friends have started the assault.

The big spending Democratic Alliance for a Better Minnesota put significant cash behind a pro-Dayton ad that began airing recently.

The Alliance, which invested considerable cash back in 2010 to bash Dayton's Republican opponent, used the ad to make a pitch for the idea that Minnesota is better off now than it was four years ago before Dayton was elected.

Television viewers this year had already seen ads trashing Dayton. Early this month, the big spending conservative Freedom Club began airing an anti-Dayton ad on broadcast television.

Updated