Change. Now, where was it that I heard that?

In discussing presidential transitions, I noted how rarely one president is elected to succeed a president of the same party. It happened only three times during the 20th century: 1908, when William H. Taft succeeded Theodore Roosevelt; 1928, when Herbert Hoover succeeded Calvin Coolidge; and 1988, when George H.W. Bush succeeded Ronald Reagan.

In each of those cases, a popular president did not seek reelection, and was succeeded by someone who had served in his administration as either vice president or secretary of a department.

It's also true of each of those instances that, four years hence, the successor failed to win a second full term. I think we can chalk that up to coincidence. If anyone thinks they see cause-and-effect there, please comment to that effect.

The obvious current question is: what does all this mean for John McCain? As I noted earlier, the retiring president is nowhere near as popular as the three named above. And McCain has not been part of George W. Bush's administration.

The main element that makes it difficult to do what McCain wants to do, is that a candidate in his position can be tarred by all of the negatives of the outgoing administration, without enjoying the advantages of incumbency. Swooping into town on Air Force One, and perhaps sprinkling a little federal grant money around, livens up a campaign trip of an incumbent president. By contrast, a senator on a leased campaign plane will probably be asked to justify the Iraq war, and might not look quite as presidential as he wants to look, in the process.

Perhaps the most heartening thought for McCain might be to consider three presidential candidates who came up just short, in their attempts to succeed a president of their party: Richard Nixon in 1960, Hubert Humphrey in 1968, and Al Gore in 2000. In the first two cases, the popular vote was very close and, of course, in the third Gore actually won a plurality of the popular vote. But in each of those cases, the opposition-party challenger put together a sufficient electoral college majority.

In each of those years, the incumbent president had issues. Dwight Eisenhower was personally popular, but the country was in recession in 1960. In 1968, Lyndon Johnson's policies were under attack from both left and right. In 2000, Bill Clinton remained popular, but Gore distanced himself from Clinton in order to avoid association with the scandal that had brought impeachment in 1998.

Still, with a few more votes in Florida, Illinois, and maybe a couple of other states ...

But, whether an incumbent is on the ballot or not, the electorate has often wanted -- guess what? Change! We will soon find out whether Barack Obama's emphasis of that theme gets him the result he wants.