Here they go again.

Oregon's Republican senators this morning declared they would walk out of the legislative session to block a bill capping carbon emissions.

Their decision followed Democrats voting to advance Senate Bill 1530 out of the Joint Ways and Means Committee—a narrow vote along partisan lines that required Senate President Peter Courtney (D-Salem) to join the committee and cast a vote. Republicans also pressed to allow a referral of the bill to ballots for a popular vote. They lost.

Republicans said Courtney's gamesmanship left them no choice but to flee the Capitol—and the state.

"Senator Courtney's actions leave no other option for Senate Republicans but to boycott and deny quorum because cap and trade is on the way to the Senate floor," said Senate Minority Leader Herman Baertschiger, Jr. (R-Grants Pass). "Democrats refused to work with Republicans and denied every amendment that was presented. Pay attention Oregon – this is a true example of partisan politics."

Senate Majority Leader Ginny Burdick (D-Portland) was equally scathing in her assessment of Republican tactics.

"Walking out on the job is a dereliction of duty," Burdick said. "Serving in the Legislature is a great honor. Walking out on the job is dishonorable and disrespectful. I am disappointed in the Senate Republicans for taking this irresponsible action."

The effect of the walkout is to deny the Legislature a quorum. Democrats control the Senate by an 18 to 12 margin but the law requires a quorum of senators be present for any floor vote—specifically, that two-thirds of members be present. That means if there are fewer than 20 senators in the building, no legislation can pass out of the Senate. (Of the 12 Republicans, the only one who showed up today was state. Sen. Tim Knopp (R-Bend).)

The decision to walk out isn't sudden. The move has been looming for weeks, with Republicans emboldened by the outrage of a vocal part of their base: rural truckers and loggers, who built a coalition called Timber Unity.

The question facing Republicans was whether that grassroots movement would overcome concerns about losing swing voters by going AWOL—a tactic that could endanger GOP senators in two swing districts, representing Salem and Bend.

If this theater seems familiar, it is: Last year, Republican senators fled to Idaho to deny Democrats a quorum on another carbon-cap bill, which died because swing district Democrats got cold feet.

Republicans hope this exodus ends similarly.

"Sometimes," said Sen. Kim Thatcher (R-Keizer), who is also running for Oregon secretary of state, "a boycott is the best way to stop bad laws from happening to good people."