Question: Al Franken's 2008 United States Senate election opponent had previously been a member of which political party before becoming a Republican?

Context paragraphs:
United States Senate election in New Mexico, 2008: The 2008 United States Senate election in New Mexico was held on November 4, 2008 coinciding with the 2008 U.S. presidential election.  Incumbent Republican U.S. Senator Pete Domenici decided to retire instead of seeking a seventh term.  All three of New Mexico's U.S. Representatives (Tom Udall, Steve Pearce, and Heather Wilson) chose to retire from the U.S. House of Representatives in order to run for the seat.  Pearce defeated Wilson in the Republican primary.  Udall won the Democratic primary unopposed and won the general election.  Udall's win ended 36 years of Republican control of this seat.

United States Senate election in Alaska, 2008: The 2008 United States Senate election in Alaska was held on November 4, 2008.  Incumbent Republican U.S. Senator and former President pro tempore Ted Stevens ran for re-election to a seventh term in the United States Senate.  It was one of the ten Senate races that U.S. Senator John Ensign of Nevada, the chairman of the National Republican Senatorial Committee, predicted as being most competitive.  The primaries were held on Tuesday, August 26.  Ted Stevens was challenged by Democratic candidate Mark Begich, the mayor of Anchorage.

The Al Franken Show: The Al Franken Show was the flagship talk show of the former talk radio network, Air America Radio.  Hosted by Al Franken, it featured commentary and interviews arguing for left-wing positions on the issues of the day, and comically poking fun at the George W. Bush Administration.  The show began as The O'Franken Factor on March 31, 2004.  Between January 3, 2006, and February 14, 2007, the show was recorded and broadcast from the 28th floor of the historic Foshay Tower in downtown Minneapolis, Minnesota.  Prior to that date it was based in New York City.  The final show was broadcast on February 14, 2007, the day Franken announced his candidacy for the United States Senate in 2008.

United States Senate election in Minnesota, 2008: The 2008 United States Senate election in Minnesota took place on November 4, 2008.  After a legal battle lasting over eight months, Al Franken from the Democratic-Farmer-Labor Party (DFL) defeated Republican incumbent Norm Coleman in one of the closest elections in the history of the Senate.  Al Franken took his oath of office on July 7, 2009, more than half a year after the beginning of his term on January 3, 2009.

Al Franken: Alan Stuart "Al" Franken (born May 21, 1951) is an American writer, comedian, and politician.  Since 2009, he has been the junior United States Senator from Minnesota.  He became well known in the 1970s and 1980s as a writer and performer on the television comedy show "Saturday Night Live".  After decades as a comedic actor and writer, he became a prominent liberal political activist.  Franken was first elected to the United States Senate in 2008 in a razor-thin victory over incumbent Republican Senator Norm Coleman, and then won re-election in 2014 over Republican challenger Mike McFadden.  Franken is a member of the Minnesota Democratic–Farmer–Labor Party (DFL), an affiliate of the Democratic Party.

United States Senate election in Iowa, 2008: The 2008 United States Senate election in Iowa was held on November 4, 2008.  Incumbent Democratic United States Senator Tom Harkin sought re-election to a fifth term in the United States Senate.  Unlike all of Harkin's previous bids for re-election, he was not challenged by a sitting United States Congressman this year, instead facing small businessman Christopher Reed, who won the Republican primary by just a few hundred votes.

United States Senate election in Indiana, 2010: The 2010 United States Senate election in Indiana took place on November 2, 2010, alongside 33 other elections to the United States Senate in other states and elections to the United States House of Representatives and various state and local elections to fill Indiana's class III United States Senate seat.  Incumbent Democratic U.S. Senator Evan Bayh decided in February 2010 to retire instead of seeking a third term shortly after former U.S. Senator Dan Coats announced his candidacy for Bayh's contested seat.  No Democratic candidate submitted enough signatures by the deadline to run, leading Democratic officials to choose U.S. Congressman Brad Ellsworth to be the nominee.  The Libertarian Party nominated YMCA instructor Rebecca Sink-Burris, who had previously run against Evan Bayh in the United States Senate election in Indiana, 1998 but with less success than in this election.  Republican nominee and former U.S. Senator Dan Coats won the open seat.

United States Senate election in Oregon, 2008: The 2008 United States Senate election in Oregon was held on November 4, 2008.  Incumbent Republican U.S. Senator Gordon H. Smith decided to seek re-election.  Smith was the only Republican Senator from the west coast (excluding Alaska) and the only Republican holding statewide office in Oregon.  He was opposed by Democrat Jeff Merkley, the Speaker of the Oregon House of Representatives, and David Brownlow of the Constitution Party of Oregon.  Merkley won by a narrow margin, with Smith not conceding until two days after the election.  Merkley became the first Democrat to win this seat when it last went to the Republicans in 1966.

United States Senate election in Arkansas, 2008: The 2008 United States Senate election in Arkansas was held on November 4, 2008.  Incumbent Democratic U.S. Senator Mark Pryor decided to run for a second term.  No Republican filed to challenge him.  His only opponent was Green Party candidate Rebekah Kennedy.  He won re-election with 80% of the vote.

Norm Coleman: Norman Bertram Coleman Jr., (born August 17, 1949) is an American lobbyist, lawyer and politician.  He served as a U.S. Senator from Minnesota from 2003 until 2009.  Before that, he was mayor of Saint Paul, Minnesota from 1994 to 2002.  Previously a member of the Democratic–Farmer–Labor Party (DFL), Coleman became a Republican in 1996.  Coleman was elected to the Senate in 2002 and served one term, losing his 2008 reelection bid by 312 votes (out of over 3 million cast).

Supporting paragraphs: United States Senate election in Minnesota, 2008 Norm Coleman
Answer: Democratic-Farmer-Labor Party (DFL)