Dick Cheney is the reason American politics is about to get more and more interesting. Mr. Cheney is, of course, the vice president. He and President Bush are about to begin their second terms. Since Richard M. Nixon won the Republican presidential nomination in 1960, the vice president has been expected to run for president. The principal exceptions have been Spiro T. Agnew and Nelson A. Rockefeller.

As a result, there is a distinguished list of modern vice presidents who didn’t become president: Hubert H. Humphrey, Walter F. Mondale, Al Gore. Don’t forget to put Nixon on that list, too, though with an asterisk; he didn’t become president until his second campaign, eight years after he left the vice presidency.

Only one modern vice president was elected directly to the White House, and that was George H.W. Bush. (Popular trivia question: Who was the only other vice president to be elected directly to the White House? Answer: Martin Van Buren.) And yet, except for Mr. Cheney, vice presidents now routinely try for the White House.

Mr. Cheney’s intention to leave public life after the end of his second term as vice president has two important implications.

The first is to create a free-for-all for the White House in 2008. For the first time in more than half a century, there is no presumptive nominee in either party – no president running for re-election and no vice president trying for the office. Every other time since the 1952 election, when a general ran against a governor, there has been at least one figure with national-office credentials in the presidential race.

The second is to raise the question whether the Cheney experiment might start a pattern – resulting in a string of presidential nominees selecting running mates who aren’t running for anything but the vice presidency.

There are immense advantages to that arrangement. There are no competing power centers in the executive branch. There is no incentive for a vice president (like Humphrey with the Vietnam War and the elder Bush with the Iran-Contra scandal) to distance himself from White House policy. There is no distraction from the business at hand in the White House as the campaign heats up in Iowa.

How much better would Bill Clinton have governed if his vice president hadn’t been trying to position himself for the office? How much less awkward would Dwight Eisenhower have been if he hadn’t been put in the position of trying to list young Nixon’s accomplishments? For that matter, how much better a candidate might Mr. Gore have been had he not had to worry endlessly about his relationship with an impeached president? How much stronger a candidate would Humphrey had been if he had not had to squirm and square his views with Johnson’s on Vietnam – and then explain why he drifted from the administration’s policies?

Now imagine for a moment that John F. Kerry, and not George W. Bush, had won the November election. Much of Mr. Kerry’s transition time would have been taken up with creating a role that preserved the dignity and the political options of John Edwards, his running mate, rather than using Mr. Edwards as a senior counselor to make the very best administration possible for America in a very troubled time. This role is something that is invented with each administration, inevitably with some dreary and implausible rhetoric saying that never before has a vice president been so indispensable.

The tension between a vice presidential office and the Oval Office is no “West Wing” fiction; it’s inherent in the relationship of a politician who is a president and another who is vice president merely because he thinks it might be a good way to become president someday.

Mr. Bush’s relationship to Mr. Cheney is completely different, which is one of the reasons that Democrats find the vice president so provocative and their inability to reach him politically so frustrating. Unlike his predecessors, Mr. Cheney is virtually immune to political punishment. He won’t have to answer for his views, decisions, or maneuvers at a town meeting in Iowa or at a candidates’ forum in New Hampshire. He can’t be made uncomfortable in public nor repudiated at the polls.

Mr. Cheney is, in effect, politically invulnerable. That might make future presidential nominees eager to find a Cheney of their own. In his peculiar political difficulties growing out of the impeachment crisis, for example, Mr. Clinton could have used a vice president whose every word wasn’t parsed for political motive. Presidential candidates may find themselves in search of someone whose loyalty is beyond question and whose motives are selfless.

In the meantime, Mr. Cheney’s reluctance to run for president himself means that the nominations of both parties are completely open. It is an unusual situation – and unusually refreshing.

That means both the Republicans and Democrats will be able to consider their candidates in a far different context than they are accustomed. No Air Force II swooping into Cedar Rapids, no immense security details fanning out into small towns in New Hampshire’s north country.

It makes for a campaign that may be determined less by the size of a candidate’s entourage and more by a candidate’s ideas. It makes for a campaign where, in the president’s party, there is more openness to start anew and where, in the opposition’s party, there is less incentive to refight battles that might be best left in the past.

It may mean, too, that the vice presidency has reached a new maturity. It could finally be a job to be done, not a stepping-stone to another one. The legacy of this administration could well come from both halves of the ticket.