INDIANAPOLIS (AP) — Indiana became the Rust Belt’s first right-to-work state Wednesday in a move that is sure to embolden advocates seeking to curtail union rights across the country. But whether other states can replicate the conservatives’ success in Indiana is less certain.

The political factors that aligned in Indiana were so unique, and it is unlikely the same thing could happen in other states — at least for now.

Gov. Mitch Daniels’ signature Wednesday on the bill that made Indiana the nation’s 23rd right-to-work state was the end of a contentious two-year political battle that included partisan bickering, lawmaker walkouts, legislative stall tactics and union protests. In the end, Indiana marked the first win for national right-to-work supporters who tried in vain last year to push the measure despite a Republican sweep of statehouses nationwide in 2010.

It also could stand as their only victory for a while, based on a mix of obstacles that have spurned advocates in other states stretching from New Hampshire to Minnesota. The very factors that made Indiana’s right-to-work campaign uniquely successful — large state House and Senate majorities and Daniels’ ability to clear one last run for governor in 2008 before mounting a unified push for the measure — also could undermine similar efforts elsewhere.

National Right to Work Committee Vice President Greg Mourad says two major obstacles have blocked his group’s progress: governors who oppose right-to-work and pro-union Republicans in state legislatures. But much of that could change in 2012 depending on how some key state elections pan out.

“The next election should tell us quite a bit,” Mourad said Wednesday afternoon.

In New Hampshire, right-to-work supporters found themselves unable to overturn a veto from Democratic Gov. John Lynch last year. Lynch is not running for re-election in November and the New Hampshire governor’s office has often been traded between Democrats and Republicans in the last few decades.

Likewise in Montana, Democratic Gov. Brian Schweitzer is term-limited against seeking re-election in November. His veto threat has stalled efforts there, Mourad said.

However in other Rust Belt states, right-to-work advocates have run up against squeamish Republicans who don’t want to pick fights with private sector unions whose influence has waned with the decline of American manufacturing, but not to a point where they are no longer a clear political threat.

Michigan’s Republican Gov. Rick Snyder, who is up for re-election in 2014, has called right-to-work “too divisive” and Michigan’s Republican Senate Majority Leader Randy Richardville said last week he doubted right-to-work would bring the economic benefits promised by supporters.

Experts say many factors influence states’ economies and that it’s nearly impossible to isolate the impact of right to work. For major industries, access to supplies, infrastructure, key markets and a skilled workforce are key factors, according to business recruitment specialists. For a state’s workers, the impact of right-to-work legislation is limited because only about 7 percent of private sector employees are unionized. Over the years, job growth has surged in states with, and without, right-to-work laws.

“They are often the problem, guys like Randy Richardville, who have been pretty comfortable with unions,” Mourad said. Mourad noted that dealing with pro-labor Republicans can mean either building large pro-right-to-work majorities around them in a chamber or voting them out of office.

Michigan’s larger union presence has also made Republican lawmakers pause more than their Indiana counterparts, who work in a state where union membership dropped by roughly 50 percent in the last decade.

Right-to-work supporters won a decisive victory in Indiana in 2006 after the right-to-work supporter Sen. Greg Walker, a Columbus Republican, unseated Indiana’s long-time Republican Senate Pro Tem Bob Garton, an ardent right-to-work opponent.

But even with the right parts, a right-to-work victory is never guaranteed, said Garton’s successor, Senate President Pro Tem David Long, Republican of Fort Wayne.

“It doesn’t come without a fight,” Long said. “It is a passionate issue and people don’t want to take that fight on.”

Meanwhile, the union backlash in other Rust Belt states in the last few months has emboldened opponents trying to bolster their defenses.

Wisconsin’s GOP-dominated Assembly passed a law backed by Gov. Scott Walker in March that strips nearly all collective bargaining rights from public-sector unions. Walker is now preparing for a recall election after opponents turned in a million signatures aimed at forcing a vote and ousting him from office. In November, Ohio voters repealed a law limiting collective bargaining rights that was championed by Gov. John Kasich and fellow Republican lawmakers.

Indiana right-to-work proponents won a second key victory in December, when Daniels switched his position on right-to-work. As a candidate for office, Daniels had promised Indiana Teamsters in 2004 he would oppose any effort to make Indiana a right-to-work state.

He explained his change as an evolution on the issue based on new facts and the ongoing problems.

“Seven years of evidence and experience ultimately demonstrated that Indiana did need a right-to-work law to capture jobs for which, despite our highly rated business climate, we are not currently being considered,” Daniels said in a statement Wednesday.

For states without all the needed pieces, supporters have resorted to work-arounds and duct tape, in their efforts to ban mandatory union fees.

Missouri right-to-work supporters are attempting to skirt Democratic Gov. Jay Nixon’s almost certain veto by moving a version of the measure that would go straight to the voters for consideration.

Likewise, in Michigan, supporters are pushing a series of measures that opponents have dubbed “mini right-to-work.” A House committee controlled by Republicans approved a bill Tuesday that would require employees to annually renew their written consent allowing certain forms of union dues to be deducted from their paychecks.

The lead sponsor of New Hampshire’s right-to-work proposal, Rep. Will Smith, Republican of New Castle, has submitted a new version of the measure that would let public employees opt out of joining a union but would then have them negotiate their own contracts.

Smith says he hopes the re-jiggered bill will win the few extra votes needed to overturn another likely veto from Lynch.

The 28-22 roll call Wednesday by which the Indiana Senate voted to give final legislative approval to the right-to-work bill.

Voting yes were 28 Republicans and 0 Democrats.

Voting no were 13 Democrats and 9 Republicans.

Alting, Banks, Boots, Buck, Delph, Eckerty, Gard, Glick, Grooms, Head, Hershman, Holdman, Kenley, Kruse, Lawson, Leising, Long, Merritt, Miller, Mishler, Paul, Schneider, Smith, Walker, Wyss, Yoder, Michael Young, Zakas

Arnold, Breaux, Broden, Hume, Lanane, Mrvan, Randolph, Rogers, Simpson, Skinner, Tallian, Taylor, Richard Young

Becker, Bray, Charbonneau, Landske, Nugent, Steele, Tomes, Waltz, Waterman