Dallas ? On the day last month that President Bush was in Houston, raising money for Republican Senate candidate John Cornyn, Vice President Dick Cheney was in Dallas, doing the same for GOP House hopeful Jeb Hensarling.

In July, Cheney made two Texas visits, one to Houston in behalf of Cornyn and another for a Dallas fund-raiser for Rep. Henry Bonilla of San Antonio.

It was typical vice-presidential campaign duty for an atypical vice president, who was picked more for his governing experience than for his political assets.

In August, Cheney did something even more unusual, virtually announcing his candidacy for re-election as Bush’s running mate.

Vice presidents traditionally sidestep that question and say it is up to the president. But in response to a question, Cheney made clear he wanted to stay on.

“I have enjoyed immensely my time with the president,” he said, calling it “the high point of my professional life, and I wouldn’t have missed it for the world.”

True, he included the cautionary notes, declaring “if the president’s willing, and if my wife approves, and if the doctors say it’s OK, then I’d be happy to serve a second term.”

Presumably, the only real doubt there concerns his health. Cheney’s wife, Lynne, seems to be enjoying life as the nation’s second lady, and Bush never has seemed anything but delighted with his vice presidential choice.

But it was health that made Cheney seem like a good prospect for a single vice-presidential term both his history of heart trouble and the fact that he had two heart-related incidents within six months of the 2000 election.

For much of the administration’s first year, there was talk that, since Cheney was unlikely to seek the presidency in 2008, Bush might seek a running mate who could extend the GOP’s hold on the White House.

When Bush tapped Pennsylvania Gov. Tom Ridge to supervise homeland security, some suggested he would be groomed for the No. 2 spot.

But it is almost always easier to keep a vice president than to get rid of him. After all, only one vice president has been replaced since the days of Franklin Roosevelt.

Bush got a lesson of the perils of change in 1992, when, according to some reports, he wanted Dan Quayle replaced as his father’s vice president.

Any such move would have stirred a ruckus between the president and the GOP’s powerful right while conservatives were mad at the elder Bush for abandoning his 1988 vow to oppose tax increases.

Similarly, in both 1956 and 1972, GOP conservatives were upset over rumors that Vice Presidents Richard Nixon and Spiro Agnew might be dropped from the GOP ticket. Both stayed.

On the other hand, enmity from conservatives and the looming challenge of Ronald Reagan in 1975 prompted President Gerald Ford, Nixon’s non-elected successor, to drop Nelson Rockefeller, his choice as vice president and the party’s most prominent liberal.

A year later, Ford moved to pacify Reagan’s backers by selecting Sen. Bob Dole of Kansas as his new running mate. But the move did little to appease disgruntled Reaganites, it upset some moderates, and the ticket lost. The displacement of Rockefeller stands as the only modern instance in which a president actually switched running mates.

On the Democratic side, there were repeated rumors in the early 1960s that President John F. Kennedy would drop his vice president, Lyndon B. Johnson. But Kennedy already had decided to keep Johnson when an assassin’s bullet prematurely ended his presidency and his life.

Carl P. Leubsdorf is Washington bureau chief of the Dallas Morning News.