The first 2008 presidential primary is nearly a year away, and the general election won't be for another 631 days. But to hear some pundits and politicians talk, you'd think the outcome was already settled. Columnist Robert Novak reports that leading Washington Democrats, buoyed by Hillary Clinton's successful debut in Iowa, are now saying their party can't lose. Bill Daley, a former Clinton commerce secretary who was Al Gore's 2000 campaign manager, is emphatic: "I don't care who the Democratic nominee is. He will become president in '08." (Mr. Daley backs Barack Obama, which may explain that politically incorrect "he.") Rep. Artur Davis, an Alabama Democrat, describes the Hillary juggernaut: "A lot of my colleagues in the Congress say privately on the floor, 'Well, I like Obama, but Hillary is going to win. We are going to have to deal with her.' "

Some Republicans go halfway to agreeing that their party isn't likely to hold the White House. Former Minnesota Rep. Vin Weber, who now serves as policy chairman for Mitt Romney, told Roger Simon of Politico.com that "I don't want to contribute to my own party's demoralization, and it doesn't necessarily mean there will be a Democratic landslide, but I think there is a thumb on their side of the scale that's not going to come off until after the next election."

History should teach us to take such claims with more than a grain of salt. While pundits will constantly remind us when they were right, they fall strangely silent when it comes to recalling their missed calls. Let's look at how the presidential field looked some 21 months before the general election, the equivalent point where we are in this cycle, in three previous campaigns.

In the event, Mr. Bush's popularity soon tanked in a bad economy. Bill Clinton, who didn't even announce for the 1992 Democratic nomination until October 1991, became the surprise nominee. Even after he won all the key primaries, Democrats were skeptical of his chances; polls showed him trailing not only Mr. Bush but independent Ross Perot. Mr. Clinton won anyway, outpolling the incumbent by better than 5.5%.

But two years later, Mr. Clinton was in deep trouble. After Republicans swept Congress in 1994, he was reduced to insisting at a news conference that "the president is relevant here." Congressional Democrats seemed to disagree. "Everyone's clinging to their own life jacket," said Sen. Barbara Mikulski of Maryland in early 1995. Polls showed Mr. Clinton losing badly to either Bob Dole or Colin Powell.

But the White House fought back. Touting popular Dick Morris-inspired micro-issues such as school uniforms and television controls for parents they built back political capital until the impasse between Congress and Mr. Clinton led to a government shutdown in December 1995. Former Clinton aide George Stephanopoulos (now with ABC News) says that Democrats, until then holding out against the Republicans' budget-limiting efforts, were very close to blinking and were thrilled when GOP congressional leaders Bob Dole and Newt Gingrich blinked first. "Whether the cause was hubris, naiveté, or a failure of nerve," Mr. Stephanopoulos wrote in his memoir, "the Republicans had blown their best chance to splinter our party; from that point on, everything started breaking our way." Mr. Clinton went on to beat Mr. Dole by 8.5%.

The 2004 election had its share of dramatic surprises. In January 2003, an ABC News/Washington Post poll showed Sen. Joe Lieberman as the clear favorite for the nomination. He had 27% of likely primary votes, followed by Dick Gephardt with 14%, John Edwards with 11% and John Kerry with 10%. Howard Dean had 3%, less than half of Al Sharpton's support.

Mr. Lieberman continued to lead or tie for first place in 35 national polls of Democrats over the next eight months. Then anti-war sentiment and the power of the Internet to raise small donations propelled Howard Dean into front-runner status. In January 2004, just days before the Iowa caucuses, a poll of 50 Democratic insiders by the National Journal found 43 of them believed Mr. Dean would be the nominee. Not one predicted that John Kerry would be their party's candidate in 2004.

In light of this history, a degree of humility is in order for anyone making predictions about 2008. Smart Democrats know that their 2006 election victory represent an opportunity, not a sure thing. They are listening to New York's Chuck Schumer, the architect of the party's Senate takeover. He writes in a new book that those who believe the party has gained the trust of the American people are "forgetting a critical truth about the election. . . . The overwhelming reason for our victory was that Bush had screwed up." Mr. Schumer warns Democrats that "unless we build on our values to generate better ideas, sharper policies and a clearer vision, we will be in trouble" in 2008.

Democrats who want to take back the White House in 2008 would do better to listen to realists like Chuck Schumer than to triumphalists like Bill Daley.