In 1999, he took part in only the second presidential impeachment trial in American history (voting to acquit Clinton of perjury but convict him on obstruction of justice). He even got a few bills passed.

All this would be enough to keep most people engaged. And after the Sept. 11, 2001, attacks, Thompson said he'd run for re-election, because it was "not the time for me to leave." But before long, he concluded that the war on terrorism could be fought without his help.

Unlike Cincinnatus, he did not relinquish power to take up his plow, but rather to resume a lucrative career of lobbying and acting. Apparently, he found sitting through makeup sessions and waiting for his next take a more rewarding use of his time than voting on legislation.

Since he began toying with a presidential race, he has been accused of laziness. But no one who has made a living as a trial lawyer, as Thompson has, can be suspected of congenital sloth. In any event, Ronald Reagan and George W. Bush have proven that the presidency does not require a grueling work schedule.

The real question is whether Thompson really wants the office and all that comes with it for four long years. The Oval Office has its own quota of dull obligations -- attending state dinners, signing off on budgets, traveling to countries no tourist would ever choose, trying to remember the housing secretary's name -- which could be excruciating to someone with Thompson's low tolerance for tedium.

Americans, meanwhile, should wonder about entrusting the job to someone who has proven unable to sustain interest in the responsibilities that come with high federal office. In weighing his candidacy, they may find that the more they see of him, the less interested they are.