As everyone already knows, the result of today’s presidential election is a foregone conclusion: For the first time in 48 years and only the fourth time in history, a sitting Member of Congress will be elected to the White House.

Neither of the candidates — Sen. John McCain (R-Ariz.) nor Sen. Barack Obama (D-Ill.) — has been governor of a state, which is generally held as the gold standard of executive experience needed for the presidency. What’s more, beyond running a presidential campaign, neither has much in the way of significant executive experience of any kind, though McCain was commanding officer of a large Navy air squadron for about a year in the mid-1970s.

But sitting lawmakers have one advantage over governors when it comes to the presidency: They know the legislature, and the legislators.

While many presidents have at one time been in Congress, the country’s experience with electing sitting lawmakers is not only limited but mixed. The first two lawmakers to move down Pennsylvania Avenue were Presidents James Garfield and Warren Harding, who went directly from the House and Senate, respectively, to the White House and then on to the pantheon of presidential mediocrity or worse. The third was President John F. Kennedy, who got off to a rocky start with the Bay of Pigs but who eventually steered the country through the perilous days of the Cuban missile crisis.

In modern times, two other lawmakers were essentially fresh off of Capitol Hill when they entered the White House, sojourning only briefly in the vice presidency before assuming the presidency. Harry S. Truman was vice president to Franklin D. Roosevelt for only a few months before Roosevelt died. Gerald Ford was plucked from the House by President Richard Nixon to serve as vice president after Spiro Agnew resigned the office, and he became president less than nine months later when Nixon resigned on Aug. 9, 1974.

Governors, points out Stephen Hess of the Brookings Institution, often have a rude awakening when they land in Washington. “The worst place to come from is being the governor of a small, one-party state where you know everyone and have been everywhere,” he said. “Washington is not Little Rock, Atlanta or Austin writ large,” he noted, referencing the state capitals where Govs. Bill Clinton, Jimmy Carter and George W. Bush groomed themselves for the presidency. One exception, he added, is Sacramento, Calif., where Gov. Ronald Reagan presided over a huge and complex state comparable to a decent-sized country.

Lawmakers enter the White House with axes to grind on Capitol Hill and often at least a few Congressional opponents who’d like to grind their own axes into them. McCain has admitted — even perhaps boasted — that he is not a likely candidate for Miss Congeniality of the Senate. Obama appears to have played the ropes in the Senate, acting as a good “listener,” acquiring mentors such as Sen. Dick Lugar (R-Ind.) and gaining the trust of leading Democrats, who asked him to spearhead an ethics reform bill, said James Thurber, director of the Center for Congressional and Presidential Studies at American University.

Thurber said Obama’s evident listening skills would serve him well on Capitol Hill if he becomes president. McCain’s style appears to entail making a decision and then trying to persuade others to follow him, Thurber said.

But whatever McCain’s tactics, he has acquired a long list of legislative achievements that Obama cannot yet claim. McCain would certainly apply his powers of persuasion to try to achieve similar results were he elected. And members of a president’s own party who are enemies tend to want to bury the hatchet with the nation’s chief executive, Thurber notes — unless they continue to get rubbed really hard the wrong way.

But Thurber, who is not backing either candidate, expressed concern that neither has held any real reins of power for much time. “Both of them are standing on the edge of a diving board, and we don’t know if either can swim,” he said. “Governors have made better managers” in the presidency, Thurber argued. Further, he noted, the next president will have to implement major legislation, such as the housing bill passed this summer and last month’s $700 billion financial bailout bill.

Lawmakers may get the false sense that they know how Washington and an administration work when all they really know is Congress. “They find out the difference between Articles I and II of the Constitution,” Hess said. “They discover, ‘Oh, that key doesn’t actually work in that door.’”

While saying a president’s management of his campaign is not a good marker of how well he will run the country, Thurber noted that Obama has had particularly strong message discipline, allowed few leaks and made very few mistakes — all qualities needed in a president.

Never, perhaps, were the benefits and pitfalls of having a former lawmaker in the White House more evident than with the man who succeeded Kennedy upon his death, Lyndon Johnson. The Texan had run the Senate as Majority Leader with masterful dexterity, and as president succeeded in ramming through much of Kennedy’s stalled agenda on civil rights and the various laws that comprised the Great Society. But Johnson’s management of the Vietnam War failed to satisfy the war’s proponents with a victory and stirred such intense and growing opposition that by the end of his presidency, the broken politician chose not to run for re-election.