Ronald Ernest Paul (born August 20, 1935) is an American author, physician and retired politician who served as the U.S. Representative for Texas's 22nd congressional district from 1976 to 1977 and again from 1979 to 1985, and for Texas's 14th congressional district from 1997 to 2013. On three occasions, he sought the presidency of the United States: as the Libertarian Party nominee in 1988 and as a candidate in the Republican primaries of 2008 and 2012. Paul is a critic of the federal government's fiscal policies, especially the existence of the Federal Reserve and the tax policy, as well as the military-industrial complex, and the War on Drugs. He has also been a vocal critic of mass surveillance policies such as the USA PATRIOT Act and the NSA surveillance programs.
Refusal to endorse the Republican nominee
At a September 10, 2008, press conference, Paul announced his general support of four third-party candidates: Cynthia McKinney (Green Party); Bob Barr (Libertarian Party); Chuck Baldwin (Constitution Party); and Ralph Nader (independent). He said that each of them had pledged to adhere to a policy of balancing budgets, bringing the troops home, defending privacy and personal liberties, and investigating the Federal Reserve. Paul also said that under no circumstances would he be endorsing either of the two main parties' candidates (McCain - Republican Party, or Obama - Democratic Party) because there were no real differences between them, and because neither of them, if elected, would seek to make the fundamental changes in governance that were necessary. He urged instead that, rather than contribute to the "charade" that the two-party election system had become, the voters support the third-party candidates as a protest vote, to force change in the election process. Later that same day, Paul gave a televised interview with Nader saying much the same again.  Two weeks later, "shocked and disappointed" that Bob Barr (the Libertarian nominee) had pulled out of attending the press conference at the last minute and had admonished Paul for remaining neutral and failing to say which specific candidate Paul would vote for in the general election, Paul released a statement saying that he had decided to endorse Chuck Baldwin, the Constitution Party candidate, for president.  Paul withdrew from active campaigning in the last weeks of the primary election period. He received 42,426 votes, or 0.03% of the total cast, in the general election.

Q: Why does he decide to refuse to endorse the republican nominee?
A: because there were no real differences between them, and because neither of them, if elected, would seek to make the fundamental changes in governance
Where the name of the nominees mentioned?
McCain - Republican Party, or Obama - Democratic Party
McCain - Republican Party, or Obama - Democratic Party