WASHINGTON -- Something rare, and potentially significant, happened in Maryland's election this week, and it had nothing to do with picking a new president.
Two incumbent congressmen, a Democrat and a Republican, were defeated in party primaries in the same state on the same day. According to the Hotline, an online political newsletter, that hasn't happened, for reasons other than redistricting, in 16 years.
The last time, it signaled the start of an anti-incumbent wave that crested two years later with the toppling of 40 years of Democratic rule in the House of Representatives.
Republican Rep. Wayne T. Gilchrest was unseated by a more conservative challenger on Maryland's Eastern Shore, while Democratic Rep. Albert R. Wynn lost to a more liberal rival in the Washington suburbs.
They were defeated "basically for not adhering to party orthodoxy. That's a significant thing," said Bruce Cain, a political scientist at the University of California, Berkeley.
"It really tells you something about this change theme," he said. "Voters may be saying, `While we're changing things at the top, we'll change some other things. ... It certainly suggests that there's no deference to incumbency, if people feel that an incumbent has taken positions that they're annoyed with."
Incumbents in Congress win re-election more than 95 percent of the time. Except for being redistricted onto unfavorable turf, they generally lose because they get pulled under by a national wave, generated by a troubled economy or an unpopular war, or fall victim to a scandal.
That's what happened when two Arkansas congressmen - both with large numbers of overdrafts in a scandal involving the House bank - lost in a 1992 primary. That year started an anti-incumbent wave that peaked in November 1994 and cost Democrats control of the House.
The Maryland primary "confirms what we've been saying all along, which is that no incumbent is truly safe in this environment," said Ken Spain, a spokesman for the National Republican Congressional Committee.
The public is giving Congress unusually low job ratings this year, but independent analysts say they don't expect changes in control of either house of Congress this year. In part, that's because Republicans are defending more vulnerable seats than the Democratic majority.
But David Wasserman, who tracks House races for the nonpartisan Cook Political Report, said the twin defeats in Maryland "would not have happened if an anti-incumbent mood had not taken root around the country."
The public has soured on both Congress and the Bush administration, he said, creating "a number of strong challenges around the country to incumbents this year."
Maryland is only the second state to hold congressional primaries in 2008 and "already we have seen two defeats. It could be a precursor to more incumbent defeats" in the primaries and in November, he added.
Only two House incumbents lost in 2006, when Republicans lost control of the House, and no Democrat was defeated in November.
The ousting of Gilchrest and Wynn reflects another trend: the growing influence of outside groups in national elections.
The conservative Club for Growth was instrumental in defeating Gilchrest, and the Service Employees International Union played a big part in toppling Wynn.
"I don't think either one of them would have lost without those outside groups," said Karin Johanson, a former official of the Democratic Congressional Campaign Committee.
Maryland's strategic location, in the backyard of the nation's capital, makes it a showcase for groups that want to be seen as bigger players on the national scene, she noted.
For whatever reason, both groups seemed to be more successful in the state than in the presidential campaign.
The Club for Growth has criticized John McCain and waged an expensive campaign against Mike Huckabee that was designed to keep his candidacy from getting off the ground. SEIU's efforts on behalf of John Edwards in Iowa and Barack Obama in Nevada also fell short.
But the union's success in promoting Donna Edwards over Wynn virtually guarantees that organized labor will have another representative likely to be sympathetic to its interests. The 4th District, in Prince George's and Montgomery counties, is one of the most Democratic in the country, making her nomination tantamount to election.
Gilchrest's defeat removes one of the last remaining Republican moderates from the House, but it might not assure the election of a more conservative replacement.
Analysts said state Sen. Andy Harris' nomination has weakened Republican chances of holding the 1st District, which takes in the entire Eastern Shore and portions of Baltimore, Harford and Anne Arundel counties.
Wasserman said the Cook Report will change the district's rating today from "Safe Republican" to "Likely Republican."
Republican committee spokesman Spain, noting that President Bush carried the district twice, said the party expects to retain the seat.