Has any sitting president dumped his VP while seeking second term to better his chances of winning? Do you thing "W" will?

Spiro Agnew had to "resign" as Nixon's VP after being indicted. Gerald Ford was appointed to take his place before Agnew's term was up.

FDR changed VPs for the 1940 and the 1944 election. (Had he not changed in 1944, Socialist Henry Wallace would have become President upon FDR's death shortly after the start of FDR's 4th term.) William McKinley changed in 1900. Both of those won re-election. Both Roosevelt's and McKinley's changing VPs led to their new VP assuming the office of President. McKinley's, VP Theodore Roosevelt, became a strong President who won the office in his own right in 1904, and FDR's VP in 1944, Harry Truman, also became a strong became President upon FDR's death, and also won the office on his own, in 1948. Grover Cleveland changed VPs for the 1888 election and lost. Ulysses S. Grant changed VP for the 1872 election, as did Lincoln for the 1864 election. Both Grant and Lincoln won re-election. Andrew Jackson also changed VPs and won re-election.* James Madison also changed VPs, and won re-election.

*John C. Calhoun, Jackson's first VP was also VP under John Quincy Adams, but resigned during Jackson first term. Jackson, asked on his deathbed if he had any regrets, said that he had only two, that he had not shot Henry Clay, nor had he hanged John C. Calhoun. I suspect he meant it. Politics was so much more fun then.

Thanks!!