The so-called "25,000-Vote Rule" has long been an accurate yardstick by which political strategists calculate the vulnerability of congressional incumbents.

The rule is elemental: If a veteran congressman's winning margin declines by more than 25,000 votes from the previous election, or if his winning margin is less than 25,000 votes in the last election, then he is the proverbial "Dead Man Walking." Also, if a newly elected congressman does not win his second election by more than 25,000 votes, he is in severe jeopardy.

As applied to Illinois' congressional delegation, the "25,000-Vote Rule" accurately forecast the defeat of 18-term Republican Phil Crane (R-8) in 2004, and it bodes ill for the re-election prospects of 16-term Republican Henry Hyde (R-6) in 2006, presuming that Hyde runs again.

In what the media termed an upset, Crane, age 73, lost his re-election bid in the largely Republican 8th U.S. House District by 9,043 votes to Democrat Melissa Bean. Crane's district encompasses the western half of Lake County, stretching from Antioch in the north to Lake Zurich in the south (including Wauconda, Grayslake, Lindenhurst and Round Lake Beach), plus the eastern half of McHenry County and parts of Schaumburg, Palatine, Barrington, Streamwood and Rolling Meadows in Cook County. This is conservative Republican territory, and the district was won by George Bush in both 2000 (with 56 percent of the vote) and 2004 (55 percent).

So how could Crane, a veteran conservative Republican, lose? Two reasons: sloth and inattention. Crane won re-election by 53,695 votes (62 percent) in 1996, by 56,628 votes (69 percent) in 1998 and by 51,141 votes (61 percent) in 2000. But then, in 2002, when Bean first challenged him, his margin skidded to just 24,649 (57 percent) -- a decline of 26,492 from his winning margin in 2000. At this point, with the "25,000-Vote Rule" doubly clanging in his brain, Crane should have embarked on a furious re-introduction campaign in 2003, spending every weekend back in his district. He failed to do so.

And, as relentlessly emphasized by Bean, Crane's "out-of-touch" complacency continued apace. Bean accused him of continuing to take junkets, often paid for by special interests, but his campaigning in the 8th District didn't accelerate. Bean kept campaigning after her 2002 defeat, and she continued to hand out seat cushions to accentuate the fact that Crane, after 35 years in Congress, was just a "seat warmer."

Washington Republicans saw the ominous portents and tried to convince Crane to retire. He refused, and by the time he finally recognized his precarious predicament last summer, it was too late. Crane attacked Bean as a liberal and a tax-hiker, but Bean, the president of a consulting firm advising high-tech companies, didn't have any public record or voting record to defend, and Crane's broadsides fell flat. The overriding issue was not Bean's alleged liberalism; instead, it was Crane's lackluster record of congressional accomplishment and slothful inattention to district needs. Bean won simply because she portrayed herself as more energetic and attentive than her foe.

It must be remembered that Crane, first elected to Congress from the North Shore in 1969 to succeed Don Rumsfeld, who is now the secretary of defense, was once a conservative "rock star," supposedly destined for greatness. He ran for president in 1980, attacked Ronald Reagan as past his prime, and presented himself as the next-generation conservative leader. But Reagan won the Republican nomination and the presidency, and Crane went into a political tailspin.

Despite his seniority, Republicans refused to make him chairman of the tax-writing Ways and Means Committee. He lacked the discipline and motivation. Despite his acknowledged intellect -- he was once a college professor -- Crane chose to be uninvolved in the congressional process, sponsoring virtually no legislation and not championing conservative causes. So, by 2004, instead of being the conservative movement's "Grand Old Man" and a political icon, Crane was just another aging, ineffectual politician. He lost because he arrogantly ignored the warning signs.

Given Bean's narrow 52-48 percent win, a gaggle of Republicans are already frothing at the mouth to run against her in 2006. The most aggressive will be Gary Skoien, the Cook County Republican chairman and the Palatine Township Republican committeeman, who was an official in Governor Jim Thompson's administration. Also mentioned are state Representative Mark Beaubien of Barrington Hills, who has served since 1996, former state representative Al Salvi, who lost races for U.S. senator in 1996 and for secretary of state in 1998, Lake County Board member Judy Martini and former U.S. attorney Fred Foreman.

Bean's hold on the seat is precarious. Even though Crane's victory margins have been diminishing, his vote totals have held steady. Crane got 141,918 votes in 2000 and 130,192 in 2004, a decline of 11,726; the Democratic candidate got 90,777 votes in 2000 and 139,235 in 2004, an increase of 48,458. This was an outpouring of anti-Crane sentiment, not anti-Republican feeling. The 8th District is still a Republican-majority district, and a Republican such as Foreman or Skoien could beat Bean in 2006. Salvi would lose.

Unlike Crane, Hyde, age 80, is an icon. Hyde has long been a champion of the pro-life movement, opposing abortion under any circumstance, and he was the chairman of the House Judiciary Committee that impeached Bill Clinton. He is much beloved among Republicans.

But Hyde's vote trajectory is not auspicious, and. he is within the parameters of the "25,000-Vote Rule." Hyde won by 63,594 votes (64 percent) in 1996, by 61,697 votes (67 percent) in 1998, by 40,447 votes (59 percent) in 2000 and by 52,476 votes (65 percent) in 2002.

But in 2004, against Democrat Christine Cegelis, an Elk Grove businesswoman, Hyde's margin plummeted to just 26,024 votes (56 percent). That falls within the "25,000-Vote Rule," as it dropped by 26,452 from 2002 to 2004, but Hyde's margin of victory is still above 25,000. Is Cegelis the next Melissa Bean?

Under House Republican rules, no chairman can serve for more than 6 years. Thus, Hyde, first elected in 1974, was termed out of his Judiciary Committee chairmanship in 2000, and he took the International Relations Committee chairmanship, which he must relinquish after 2006. So, unlike the ostrich-like Crane, the more politically astute Hyde is likely to retire in 2006.

The 6th U.S. House District encompasses the northeastern corner of DuPage County, including Bensenville, Wood Dale, Itasca, Roselle, Elmhurst, Lombard, Villa Park, Bloomingdale, Glendale Heights and Glen Ellyn, plus, in Cook County, Rosemont, Des Plaines and parts of Park Ridge and Glenview in Maine Township and Elk Grove, Mount Prospect, Arlington Heights and part of Rolling Meadows in Elk Grove Township.

Cegelis is set to run again in 2006, but if Hyde retires, the Republican field is muddled. State Senators Dan Cronin and Peter Roskam want to run, as does DuPage County Board member Brien Sheahan. Elmhurst Mayor Tom Marcucci, state Representative Rosemary Mulligan of Des Plaines and DuPage County Board chairman Bob Schillerstrom also are potential candidates.

There are several dynamics in play: Schillerstrom, who lives outside the district in Wheaton but who can still run, yanked DuPage County out of the Suburban O'Hare Commission and expressed support for O'Hare runway expansion. Marcucci is opposed to expansion. Schillerstrom is more likely to run for statewide office in 2006. Cronin's brother ran for state's attorney in the primary against Joe Birkett in 1996, and that is remembered. Mulligan is pro-choice, and in a field of DuPage male pro-life candidates, she would have an advantage.

So it comes down to this: More than 60 percent of the 6th District's population and almost 70 percent of the Republican primary vote comes from DuPage County. If DuPage County Republicans unite behind one candidate, Mulligan has no chance. If they don't, she can be nominated. Expect Marcucci to be the consensus choice, and to beat Cegelis in 2006.

As for other Illinois Republicans, the "25,000-Vote Rule" makes them unbeatable. In the North Shore 10th U.S. House District, Mark Kirk initially won election in 2000 by 5,658 votes; he upped that to 70,311 in 2002 and to 77,657 in 2004. In the Will County-area 11th District, Jerry Weller, first elected in 1994, won by 28,899 votes in 2000, by 55,299 in 2002 and by 51,156 in 2004. In the Champaign-Urbana 15th District, Tim Johnson won by 15,264 votes in 2000, by 70,519 in 2002 and by 64,899 in 2004. And in the far Downstate 19th District, encompassing East Saint Louis and the surrounding rural areas, John Shimkus won by 1,238 votes in 1996, by 44,628 in 1998 and by 67,011 in 2000; he beat another incumbent in 2002 after the redistricting by 23,439 votes and then upped that to 118,851 votes in 2004. Shimkus is a likely candidate for Illinois state treasurer in 2006.