It happened again Tuesday, as Travis Childers beat Greg Davis in a special election to replace Republican Roger Wicker, who served in the House since 1994 and was appointed to the U.S. Senate to fill the seat vacated by Trent Lott.
Childers' win will give him the chance over the next several months left in the seat's two-year term to build a fundraising and publicity advantage as he heads into November's general election. He will again face Davis, as well as two other opponents.
Childers' win gave Democrats a 236-199 edge over Republicans in Congress.
Earlier this year, Democrats captured the Illinois district long represented by former Republican Speaker Dennis Hastert, who resigned from Congress. This month, Democrats claimed a seat in Louisiana that Republican Rep. Richard Baker vacated and that the GOP had held since 1974.
Childers is a socially conservative county official, while Davis is mayor of a fast-growing city across the state line from Memphis, Tenn.
Vice President Dick Cheney campaigned for Davis the day before the special election, and Davis ran ads trying to tie Childers to Barack Obama, House Speaker Nancy Pelosi, and the national Democratic Party's policies.
Childers stressed his independence, emphasizing his support of gun rights and opposition to abortion. He said his values match those of most voters in the deeply conservative district.
Tom Cole, chairman of the National Republican Congressional Committee, said the Mississippi race showed that "Republicans must be prepared to campaign against Democrat challengers who are running as conservatives, even as they try to join a liberal Democrat majority."
Cole said voters are "pessimistic about the direction of the country and the Republican Party in general" and the GOP must offer "positive change."
Marty Wiseman, a political scientist at Mississippi State University, said if Democrats can carry districts that traditionally have been safe bets for the GOP, "Republican strategists have to be terrified."
"If you think about the House and the Senate ... and the number of Republican Senate seats that are exposed, this could turn into something bigger than the presidential race this fall," Wiseman said.
Elsewhere, in right-leaning Nebraska, Republican Mike Johanns, the former U.S. agriculture secretary and Nebraska governor, easily won the Republican primary Tuesday in a race to replace retiring Republican Sen. Chuck Hagel. On the Democrat side, Scott Kleeb beat three other Democrats.
And in West Virginia, a conflict-of-interest scandal derailed the state's top judge from serving another term. With 97 percent of precincts reporting, Chief Justice Elliott "Spike" Maynard, once considered a shoo-in for re-election, was third in a field of four candidates.
The two top vote-getters will face the lone Republican in the race for two high court spots in November.
Maynard lost his advantage when photos surfaced in January of him vacationing with the chief executive of a massive coal producer. He faced a former justice, a Huntington lawyer and a West Virginia University law professor.
Maynard raised the most money, and his allies included the state's chamber of commerce and medical association. But the photos taken during a 2006 Monaco vacation, when he met up with Massey Energy Co.'s chief executive, quickly became campaign fodder.
Maynard blamed the furor on political foes, but withdrew from several Massey-related cases. He had said he would do the same if re-elected.
West Virginia Sen. Jay Rockefeller, who hasn't lost a statewide race since 1972, easily beat two challengers as he seeks a fifth six-year term. He'll face Republican Jay Wolfe in November's general election.
Gov. Joe Manchin easily fended off a primary challenge and will take on Republican Russ Weeks, a former state senator, in November.