A treasure trove of data on the meaning of the 2004 presidential election has just been released, and you can bet that if reporters don’t look at it carefully, strategists for potential candidates will. The 2004 election numbers may explain why Hillary Clinton is taking care to present herself as a centrist.

While we vote for president in local precincts and then see the election results reported by state and county, the way to get a feeling for the underlying trends of an election is to wait for the results to be broken down into the nation’s 435 congressional districts. Only a handful of states adequately compile presidential election results by congressional districts. That’s why political junkies appreciate the efforts of Polidata, a database firm run by Clark Bensen, which just spent months collecting precinct-level data from local officials and belatedly giving a fresh perspective on how George W. Bush assembled his winning coalition.

In 2000, Mr. Bush carried 228 congressional districts to Al Gore’s 207 on his way to one of the closest victories in American history. This year Mr. Bush carried 255 congressional districts, nearly six in 10. The number of “turnover” districts – those voting for a House member of one party and a presidential candidate of the other – continues to shrink, mostly due to the growth of straight-ticket voting and gerrymandering. There were only 59 such districts in 2004, compared with 86 in 2000 and 110 when Bill Clinton beat Bob Dole in 1996.

The best chances for Democrats to gain the 15 seats they need to take control of the House in 2006 are in these districts held by “Kerry Republicans.” The problem is that there are so few of them. John Kerry carried just 18 GOP House members’ districts, while Mr. Bush carried 41 Democratic ones.

Only five Republican House members currently sit in districts where Mr. Bush won less than 47% of the presidential vote last year: two in Connecticut, two in Iowa and one in Delaware. But 31 House Democrats represent districts where John Kerry won less than 47%. That means Republicans have many more opportunities to pick up seats in favorable political terrain as Democratic members leave the House. No one expects Democrats to hold the seat of Ike Skelton of Missouri when he leaves office; President Bush won 64% of his district’s votes. Ditto for the district of Gene Taylor of Mississippi, where Mr. Bush won 68%.

Another worrisome sign for Democrats is the Hispanic vote. Michael Barone, a co-author of the definitive Almanac of American Politics, reports that Polidata’s findings tend to confirm the exit polls that showed George W. Bush gaining nine percentage points among Hispanic voters, ending up with some 44%. Several liberal-oriented groups disputed those numbers, but a look at the breakdown of the two dozen districts with Hispanic House members shows that Mr. Bush indeed made strong gains in their districts.

Take Texas, where six of the state’s 32 House districts have Hispanic representatives (five Democrats and one Republican) and another 69%- Hispanic district is represented by Anglo Democrat Lloyd Doggett. In the areas that now make up those seven districts, Mr. Bush dramatically increased his vote totals over 2000, winning four of the seven districts and breaking even in their total popular vote. In two of the Democratic Hispanic districts, Mr. Bush won 55% of the vote, setting up the possibility that a Republican could win those seats when they become vacant.

In Florida, Mr. Bush’s Hispanic percentages were artificially inflated in 2000 by Cuban-American anger over the Clinton administration’s deportation of Elian Gonzalez. But Mr. Bush still did well in the three Miami-area districts represented by Cuban-American Republicans, winning them by an average of 12 percentage points.

But it is in California where Mr. Bush made the most surprising gains among Hispanic voters. Ten of the Golden State’s 53 districts are held by Hispanic Democrats, and two others, in the Central Valley, by Portuguese-American Republicans. In the 10 Democratic districts, Al Gore won 65% of the vote in 2000. But in last year’s election, Mr. Bush made gains in every district and ended up with about 40% of the overall vote in those 10 districts.

In 2000 Mr. Bush lost what is now the Orange County district held by Democrat Loretta Sanchez by 15% of the vote. In 2004, Mr. Bush outpolled Mr. Kerry in Ms. Sanchez’s district. Similarly, Mr. Bush captured the Modesto-based district of Democrat Dennis Cardoza, an area that Al Gore had easily carried. “I fully appreciate the fact that George W. Bush won 49% of my district,” says Jim Costa, a Fresno-area freshman Democrat who won only 54% last November against an Anglo Republican.

True, Hispanic voters were attracted to Mr. Bush for reasons that may not easily transfer to other Republicans. “He is seen as simpatico in terms of his strong religious faith, his willingness to speak some Spanish, school choice and a desire to help small business owners prosper,” says Martha Montelongo, a talk show host in California. Obviously, calls for Republicans in government to crack down on illegal immigration can create cross-pressures that could endanger GOP support among Hispanics, but those are often exaggerated. Hispanics rank immigration low among their list of priority issues, and last November exit polls show that 47% of Hispanics in Arizona voted for Proposition 200, a measure designed to limit government services to illegal immigrants and prevent them from voting. “The Hispanics who voted for George Bush largely reject identity politics and simply want to be respected, rather than pandered to,” says Ms. Montelongo.

The Polidata numbers show areas of Republican weakness, too. Mr. Bush continued to lose ground in university towns and among upper-income Protestants. Mr. Barone notes that the president won only 54% of the vote in Greenwich, Conn., the tony town that revered his grandfather and its senator, Prescott Bush. “Episcopalians have a declining use for George Bush,” says Mr. Barone.

But Democrats should worry that those losses were more than compensated by his gains among Hispanics, rural Democrats and Italian-Americans. In the Brooklyn, N.Y., district represented in the House by Anthony Weiner, a former aide to Senator Chuck Schumer, Mr. Bush won 44% of the vote in a district that contains many white ethnic and Orthodox Jewish neighborhoods. In 2000, Mr. Bush had won only 30%.

It’s no accident that Mrs. Clinton, who will be running for re-election in New York next year before she launches her presidential campaign, is talking about the importance of religious faith and reaching out to moderate voters. “She pores over political data as carefully as Bill Clinton ever did,” says New York Democratic strategist Hank Sheinkopf. A close look at the Congressional district results from last year is convincing many Democrats that a move to the middle may be more than a smart media strategy. It may be a matter of political survival.

Mr. Fund is the author of “Stealing Elections: How Voter Fraud Threatens Our Democracy.” To subscribe to the “Political Diary” e-mail newsletter featuring Mr. Fund, please visit www.OpinionJournal.com, from which this column is excerpted. © Dow Jones & Company Inc.