PORTLAND – Part of a national political spending network co-founded by a top Republican strategist has entered Maine’s U.S. Senate race with a reported $309,000 ad buy against independent Angus King.

The ad started Tuesday and will air for a week.

Crossroads GPS, a nonprofit arm of the American Crossroads super political action committee, said in a prepared statement that it will spend $309,000 in Maine broadcast and cable markets.

The ad criticizes King’s record as Maine’s governor from 1995 to 2003, saying he increased taxes, slashed school funding and increased state spending.

In an interview, American Crossroads spokesman Nate Hodson called King “a liberal senator who would caucus with the Democrats” in the Senate.

“More than anything, you look at Angus King’s record and how detrimental that would be to the state of Maine in the U.S. Senate,” Hodson said. “American Crossroads is focused on winning a majority and we think it’s important to keep a Republican in this seat.”

Getting a jump on the ad’s release, King’s campaign sent an email to supporters Monday evening using the ad as a plea for campaign donations.

The email’s subject line was “Karl Rove,” a Republican political operative who co-founded American Crossroads. He worked in President George W. Bush’s administration and led his two successful presidential campaigns.

“Karl Rove is a notorious partisan and part of the huge divide in Washington,” said King’s spokeswoman Crystal Canney. “Angus King is a threat because no one owns him or his vote.”

In the email, King’s campaign manager, Kay Rand, said the ad against King would be “deceitful” and implored supporters to help King “fight back against this onslaught.”

She said the campaign thought the ad buy would be $350,000.

Canney said the fundraising pitch worked and the campaign raised “several thousands” of dollars after the email went out.

Records at Portland’s CBS affiliate, WGME-TV, show that more than $168,000 of the group’s airtime against King was bought in the Portland market — 35 percent at NBC affiliate WCSH, 29 percent at ABC affiliate WMTW, 26 percent at WGME and 10 percent at Fox affiliate WPFO.

Last week, the Sunlight Foundation, a campaign finance website, said American Crossroads has spent $174 million nationally on the 2012 election, which should ensure that it will be “the most influential outside group in this election cycle.”

Drew Brandewie, a spokesman for King’s top opponent, Republican Charlie Summers, said in a statement that “the more Mainers learn about King’s financial mismanagement” and record, “the more his support shrinks.”

Staff Writer Michael Shepherd can be contacted at 621-5632 or at:

mshepherd@mainetoday.com