LANSING, Mich.  —  The state Senate passed a bill Wednesday setting up a Jan. 15 presidential primary, but Michigan Democrats continued to fight among themselves over whether to hold a primary or a caucus.

The bill passed 21-17, with all Republicans voting for it and all Democrats voting against.

State Democratic Chairman Mark Brewer said the bill contains language that doesn't comply with national Democratic rules, so it's unacceptable. The bill is expected to be changed once it reaches the Democrat-controlled House.

If Michigan moves to a Jan. 15 primary, it's likely Iowa and New Hampshire would move up their first-in-the-nation contests.

A number of prominent Michigan Democratic political leaders, including Gov. Jennifer Granholm, favor holding a closed presidential primary with the Republicans. State GOP Chairman Saul Anuzis has agreed on a Jan. 15 presidential primary if Democrats can agree to hold one.

But not all Michigan Democrats favor a primary. Backers of former North Carolina Sen. John Edwards want to hold a caucus because they think that will increase the influence of union members who back him.

U.S. Rep. Bart Stupak, a Menominee Democrat who supports Edwards, said in a letter released Tuesday night that he opposes a presidential primary.

He didn't mention Edwards, instead saying it would be irresponsible to hold an expensive, state-paid presidential primary at a time when the Michigan budget is so strapped. If a primary wasn't held, the state Democratic Party would pay the costs of a caucus, while the state GOP would pick up the tab for a presidential nominating convention.

"It is inappropriate for the state legislature to vote to fund an unnecessary political presidential primary and then ask taxpayers to increase their taxes because the state is broke!" Stupak wrote. He said he'd support a statewide primary only if the cost was borne by the presidential candidates or state party organizations.

Democratic leaders who support a primary were drafting their own letter saying the cost of a primary was worth it because voter turnout would be so much higher.

More than 1 million people voted in Michigan's 1992 presidential primaries, compared to about 160,000 who voted in the Democratic presidential caucuses in 2004, a year in which no GOP primary was held. About 5,000 GOP delegates would choose a Republican nominee at a state convention next year if a joint primary isn't held.

As Michigan took another step toward a Jan. 15 primary, South Carolina Democratic Chairwoman Carol Fowler said she would not ask to move her state's primary date. The calendar jumping is an issue the Democratic National Committee's rules committee will take up this weekend, she said.

South Carolina Democrats are scheduled to hold their primary Jan. 29 — the same day as Florida, which moved up its primary despite a threat from both national parties that they would withhold half the state's delegates to next summer's national conventions.

South Carolina Republicans recently leapfrogged Florida and move their primary to Jan. 19 from Feb. 2 to maintain their first-in-the-South status. South Carolina GOP Chairman Katon Dawson says he's not moving his party's primary regardless of what Michigan does.

"As long as we're first in the South, we're solid on the 19th," he said. "If a Southern state tries to move before our historical preference of the first primary in the South, we're prepared to move — and we can move — on an hour's notice."

He's irked, however, that South Carolina's primary now may end up in Michigan's shadow. If Michigan moves, it may mean he has to set a different date for the final pre-primary presidential debate in South Carolina.

No date has been publicly announced, but "I'm thinking about moving the date right now," Dawson said.