Longtime Republican Senator Lamar Alexander, a former presidential candidate and two-term Tennessee governor, said on Monday he will not seek re-election in 2020."The people of Tennessee have been very generous, electing me to serve more combined years as governor and senator than anyone else from our state," he said in a statement. "I am deeply grateful, but now it is time for someone else to have that privilege."Alexander was first elected to the U.S. Senate in 2002 and has been re-elected two times. He ran for the Republican presidential nomination in the 1996 and 2000 elections, becoming famous for the plaid "lumberjack" shirt he sported throughout his campaign.Alexander served in Senate Republican leadership positions in the past. On leaving those roles, he said he wanted to try to carve out a niche as a bridge between warring factions on issues ranging from curtailing greenhouse gas emissions blamed for climate change to comprehensive immigration reform.More recently, he tried to craft a compromise to an Obamacare replacement bill. Those efforts, however, yielded little success in an increasingly divided political climate.Outside elected office, he was president of the University of Tennessee and Education Secretary under President George H.W. Bush.Alexander is a classical and country pianist, author and grandfather of nine, according to the official biography on his Senate website.