Question: What committee did an American politician and veterinarian, that predicted the United States Senate election in Alaska, 2008 would be competitive, serve as chairman for? 

Context paragraphs:
United States Senate election in Alaska, 2004: The 2004 United States Senate election in Alaska took place on November 2, 2004 alongside other elections to the United States Senate in other states as well as elections to the United States House of Representatives, various state and local elections, and the presidential election of that year.  Incumbent Republican U.S. Senator Lisa Murkowski of Anchorage, sought election to her first full term after being appointed to serve out the rest of her father's unexpired term when he resigned in December 2002 to become Governor of Alaska.  Her main challenger was Democratic former Governor Tony Knowles, her father's predecessor as governor.  Murkowski won by a slight margin.

United States Senate election in Alaska, 2014: The 2014 United States Senate election in Alaska took place on November 4, 2014, to elect a member of the United States Senate to represent the State of Alaska, concurrently with the election of the Governor of Alaska, as well as 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.

United States Senate election in Alaska, 1986: The 1986 United States Senate election in Alaska was held on November 3, 1986.  Incumbent Republican United States Senator Frank Murkowski ran for a second term in the United States Senate and was primarily opposed by Alaska Pacific University President Glenn Olds.  Following a highly competitive election in 1980, Murkowski faced a legitimate opponent in Glenn Olds, and the contest was fairly close.  However, in the end, Murkowski was able to defeat Olds by a slightly wider margin than he won by six years prior.

United States Senate election in Alaska, 2002: The 2002 United States Senate election in Alaska was held on November 5, 2002.  Incumbent Republican United States Senator Ted Stevens ran for and won a sixth term in the United States Senate.  He faced perennial candidate Frank Vondersaar, the Democratic nominee, journalist Jim Sykes, the Green Party nominee, and several other independent candidates in his bid for re-election.  Ultimately, Stevens crushed his opponents to win what would be his last term in the Senate, allowing him to win with the largest margin of victory for any Senate election in Alaska, as well as the highest percentage of the vote in any of his elections.

United States Senate election in Illinois, 1966: The 1966 United States Senate election in Illinois took place on November 8, 1966.  Incumbent Democratic United States Senator Paul Douglas, seeking a fourth term in the United States Senate, faced off against Republican Charles H. Percy, a businessman and the 1964 Republican nominee for Governor of Illinois.  A competitive election ensued, featuring campaign appearances by former Vice-President Richard M. Nixon on behalf of Percy.  Ultimately, Percy ended up defeating Senator Douglas by a fairly wide margin, allowing him to win what would be the first of three terms in the Senate.

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 Alaska, 2016: The 2016 United States Senate election in Alaska was held on November 8, 2016 to elect a member of the United States Senate to represent the State of Alaska, concurrently with the 2016 U.S. presidential election, as well as 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.

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.

United States Senate election in Alaska, 1984: The 1984 United States Senate election in Alaska was held on November 6, 1984.  Incumbent Republican Senator Ted Stevens sought re-election to a third term in the United States Senate.  Owing to his popularity and the conservative bent of Alaska, Stevens did not face major opposition, and easily crushed former Alaska Attorney General John Havelock in the general election.

John Ensign: John Eric Ensign (born March 25, 1958) is an American veterinarian and former politician based in Las Vegas, Nevada.  He was a Congressman and United States Senator from Nevada, serving in the latter seat from January 2001 until May 2011.  He resigned amid a Senate Ethics Committee investigation.

Supporting paragraphs: United States Senate election in Alaska, 2008 John Ensign
Answer: National Republican Senatorial Committee