OLYMPIA – Republican state Rep. Rodney Tom switched parties Tuesday and will challenge state Senate Republican Floor Leader Luke Esser this fall.

An irritated state Republican Chairwoman Diane Tebelius demanded that Tom resign his House seat, but Tom said he intended to serve the balance of his term as a Democrat.

Democrats, including Gov. Chris Gregoire, welcomed the convert. Gregoire personally called him to chat. The Democratic Party said Tom’s switch reflects a growing disenchantment of suburban moderates with hard-line Republicans.

Esser and the Republicans said the Medina lawmaker’s decision came out of the blue. The GOP is a “big tent” party and moderates were always welcome, they said. Some suggested that political ambition was the root cause.

Tebelius said she was “totally shocked.” She called for his resignation, saying he was elected twice as a Republican and that his “calculating change of mind demonstrates a lack of credibility and sincerity.” Republicans haven’t changed, Tom has, she said.

Tom replied, “I’ve been elected by Republicans, Democrats and independents. No way am I resigning. It’s not going to happen.”

Tom, 42, said he had been mulling the switch for months and even thought about filing as a Democrat two years ago. He said Democrats have been wooing him, knowing of his differences with his caucus.