Washington ? Party-switching Sen. Arlen Specter fell to a younger and far less experienced rival in the Pennsylvania Democratic primary, and political novice Rand Paul rode support from tea party activists to a Republican rout in Kentucky on Tuesday, the latest jolts to the political establishment in a tumultuous midterm election season.

In another race with national significance, Democrat Mark Critz won a special House election to fill out the term of the late Democratic Rep. John Murtha in southwestern Pennsylvania. The two political parties spent roughly $1 million apiece hoping to sway the outcome there, and highlighted the contest as a possible bellwether for the fall when all 435 House seats will be on the ballot.

On the busiest night of the primary season to date, Arkansas Democratic Sen. Blanche Lincoln was forced into a potentially debilitating June runoff election against Lt. Gov. Bill Halter in her bid for nomination to a third term. Rep. John Boozman won the Republican line on the ballot outright.

Taken together, the evening’s results were indisputably unkind to the political establishments of both parties — with more contested primaries yet to come, particularly among Republicans.

But any attempt to read into the results a probable trend for the fall campaign was hazardous — particularly given Critz’s victory over Republican Tim Burns to succeed Democrat Murtha in Congress.

Specter, seeking his sixth term and first as a Democrat, fell to two-term Rep. Joe Sestak, who spent three decades in the Navy before entering politics. Sestak was winning 54 percent of the vote to 46 percent for Specter. He told cheering supporters his triumph marked a “win for the people over the establishment, over the status quo, even over Washington, D.C.”

Sestak’s campaign calling card was a television commercial that showed former President George W. Bush saying he could count on Specter, then a Republican, and then had Specter saying he had switched parties so he could win re-election. Once unleashed, it coincided with a steady decline in Specter’s early lead in the polls and signaled the end of the political line for the most durable politician of his generation in Pennsylvania.

Former Rep. Pat Toomey won the Republican nomination and will run against Sestak in the fall in what is likely to be one of the marquee races in the battle for control of the Senate.

Among Republicans, Paul’s victory over Secretary of State Trey Grayson was a rebuke to the GOP Senate leader, Mitch McConnell. McConnell recruited Grayson to the race after pushing the incumbent, Sen. Jim Bunning, into retirement out of concern that he would lose the seat to the Democrats.

Kentucky marked the third time that tea party activists, a collection of disparate groups without a central political structure, have placed their stamp on Republican races.

Their votes at a Utah Republican convention helped deny a spot on the ballot to Sen. Bob Bennett, a conservative judged as not sufficiently so. And their backing helped propel one-time longshot Republican Marco Rubio to a lead in the pre-primary polls in Florida’s Senate race, prompting Gov. Charlie Crist to quit the party and run as an independent.

Before Specter’s defeat, West Virginia Democratic Rep. Alan Mollohan was the only incumbent in his party to lose a primary.