Former State Rep. Ron Erhardt of Edina is angling for a comeback -- as a DFLer. The leader of the rump Republican group that helped DFLers override Gov. Tim Pawlenty's 2008 transportation bill veto was dumped by his GOP party in 2008. He ran as an independent and came in second in what may have been the year's most-watched legislative contest. It was won by Republican Rep. Keith Downey; DFLer Kevin Staunton placed third.

Erhardt, who served 18 years in the House and was once one of the state Republican Party's most prolific fundraisers, sent letters to DFL activists this week announcing his party change. He said he intends to challenge Staunton, who is also running again, for DFL endorsement. Erhardt is not yet saying whether he'll take his comeback bid to the primary voters if he doesn't prevail at the endorsing convention.

Erhardt's experience, and that of the other five GOP transportation bill overriders, illustrates the high cost today's political parties are exacting for cooperation with the opposition party. Only one of the Override Six was reelected in 2008 without an intra-party challenge; only two of them still serve in the state House.

This year, a group of DFLers in Winona are exhibiting a similar insistence on strict party discipline. They're backing Winona City Council member Debbie White over 12-term Rep. Gene Pelowski, DFL-Winona. Pelowski's vote against a DFL attempt to override Pawlenty's 2009 tax bill veto is a factor in their effort to unseat him.

Minnesota voters have split the levels of power at the statehouse between two or more parties for the past 20 years, evidently expecting elected officials to exhibit enough bipartisanship to govern. But during the same years, political parties' tolerance of bipartisan action by their elected officials has diminished. It's no wonder that political parties in this state and nation look increasingly not like the facilitators of democratic governance that they are supposed to be, but like impediments.