MADISON, Wis. -

A Democratic state senator said he has quit his party's caucus after Majority Leader Mark Miller offered him a weak committee chairmanship post.

Sen. Tim Cullen, D-Janesville, said Miller insulted him by offering him the chairmanship of the Small Business and Tourism Committee. Cullen turned the position down, saying the panel doesn't matter, and Miller responded by making him the only Senate Democrat without any committee chairmanship.

"It's so blatantly aimed at me, it's so blatantly intended to send a message that I'm not welcome," Cullen said. "If you know me, you'd know I wouldn't just take it."

Cullen, a moderate who was the Senate's majority leader in the 1980s, said he will no longer join Senate Democrats' meetings and is leaning toward becoming an independent.

If Cullen leaves the party, the Democrats would still maintain a majority because Sen. Rich Zipperer, R-Pewaukee, has decided to leave the Senate for a post in Gov. Scott Walker's administration.

The Senate just switched hands following a recall election, leaving Democrats with a 17-16 majority. That will jump to 17-15 next month after Zipperer leaves.

Even if Cullen becomes an independent, Democrats would still have a 16-15-1 majority.

Miller refused an on-camera interview through a spokesman Tuesday afternoon, instead issuing a four-sentence statement.

"I am disappointed in Sen. Cullen and the decision he made today," Miller wrote. "Sen. Cullen turned down the chairmanship of the Committee on Small Business Development and Tourism.

"He told me that if that was the committee offered to him, he would rather chair no committee at all. It was an important committee as small business is the economic engine for Wisconsin."

Cullen told Senate colleagues that the offer was "minimal, unacceptable."

"Small Business and Tourism are enormously important to the economy, without question," Cullen told WisPolitics.com. "But in the state Senate, historically, Small Business and Tourism have not been very significant committees at all and people who've been around here know that."

Sen. Scott Fitzgerald, R-Juneau, said he wanted to talk with Cullen later this week. The rift surprised him, Fitzgerald told WISC-TV.

"Sen. Miller has continued to march his caucus to the beat of a very left-wing drum, and I don't know that all the senators kind of fit that mold," he said.

The importance of the committee assignment that Cullen turned down is "in the eye of the beholder," Fitzgerald said, adding that senators view different committees differently based on their backgrounds.

Cullen said he would not vote consistently with either party going forward, and that he expects to run again when his term is up in 2014.

His moderate views on issues, such as how long the Senate Democrats should've stayed in Illinois during the collective bargaining bill, led to the split with leaders, he said.

"The thing where I differ from my (former) caucus is that I thought we stayed there too long," he said. "I thought going there for 7-10 days to wake up the state was the right thing to do, and I'll still believe that."

Sen. Dale Schultz, R-Richland Center, a moderate in his own party, indicated he would not follow his friend and consider leaving the Republican caucus, but that he would continue to work with Cullen.

"We'll continue trying to set an example of how to work across party lines and get things done," Schultz said. "I believe that's what folks are yearning for; bold leadership that sets party politics aside for the betterment of citizens."

Cullen said the image of a united front of 14 Senate Democrats during the collective bargaining debate is history.

"These are a whole new series of events, and that's now a time in the past," he said.