Republican U.S. Sen. David Vitter’s turnaround on Common Core — he now opposes the standards — has reignited debate on the volatile topic four months before legislative arguments begin in earnest.

Many opponents of the overhaul concede that 2015 likely is the last best chance to shelve the new guidelines in reading, writing and math.

“The window of opportunity is the spring session 2015,” said state Rep. Brett Geymann, R-Lake Charles, one of the leaders of the anti-Common Core forces.

Barry Erwin, president of the pro-Common Core Council for a Better Louisiana, agreed. “Practically speaking, it is next year or bust for them,” Erwin said of the opponents.

After six months of arguments in and outside the Louisiana Legislature, things have been mostly quiet on the Common Core front since Aug. 20.

That is when 19th Judicial District Court Judge Todd Hernandez, of Baton Rouge, issued an injunction that paved the way for students to be tested on the standards in the spring.

While appeals on that and other anti-Common Core lawsuits are pending, the new academic guidelines are a fact of life in public schools statewide.

But Vitter announced on Dec. 1 that he now opposes Common Core, just four months after he endorsed the academic guidelines.

After listening to parents, teachers and others, he said, “I don’t believe that we can achieve the Louisiana control, buy-in and success I’m committed to if we stay in Common Core.”

Vitter’s latest opinion on the issue sparked charges that he did an about-face to boost his 2015 campaign for governor.

A wide range of business groups, including CABL, the Louisiana Association of Business and Industry and ExxonMobil, have reiterated their support for the standards.

“Political winds blow in different directions,” those and other firms said in a prepared statement. “But Louisiana’s children should not pay the price for that in ways that limit their opportunities and leave them even further behind students in most other states.”

Lt. Gov. Jay Dardenne, a Republican who also is running for governor, renewed his support for Common Core in the wake of Vitter’s reversal. “If ever there is an issue where we need consistency in the leadership of the state, it is the education of our children,” Dardenne said.

What it all means is that, when Common Core arguments resume as the 2015 session convenes on April 13, the political landscape will be much different from the 2014 gathering.

Gov. Bobby Jindal, another GOP leader who went from backing to opposing the standards, is expected to actively back Common Core repeal efforts after offering only tepid support for those efforts earlier this year.

Geymann said Vitter’s reversal could prompt some state lawmakers to do the same, especially because Vitter is one of the favorites to win the race for governor. “I think we are in a stronger position than we were last year,” he said.

“He (Vitter) is hearing around the state what we are hearing, and the legislators are hearing from the same people,” Geymann said. “We think a lot of legislators have moved our way or are at least willing to listen.”

Common Core backers have different views on what Vitter’s opposition will mean.

“I don’t see it as changing the landscape a lot,” Dardenne said. “I don’t think Vitter’s opposition moves a lot of legislative votes.”

He said repeal would be a huge mistake.

“It is a recipe for chaos in education,” Dardenne said.

A spokesman for Vitter did not respond to a request for comment.

What impact shelving the standards would have is in dispute.

Replacing the standards and assessments would cost the state up to $25 million over the next five years and local school districts even more, according to a March memo by officials of the state Department of Education.

Geymann disagrees. “The truth is the disaster is right now,” he said.

Erwin said Vitter’s stance carries weight.

“When you bring someone in with his stature, it does change the environment,” he said.

The race for governor will unfold in 2015; the new governor takes office in January 2016.

The calendar raises the specter of Louisiana’s top two politicians — Jindal and Vitter — sharing a goal of repealing Common Core amid efforts to enhance their presidential and gubernatorial prospects, respectively.

“I think the big question is to what degree does he (Vitter) choose to get involved in the session, especially given the fact that the governor is going to make an all-out effort during the coming session,” Erwin said.

“And they have not been the closest political allies,” he noted.

Senate Education Committee Chairman Conrad Appel, R-Metairie, who backs Common Core, said it is too early to tell whether efforts to repeal the new standards will succeed in 2015.

“I think Louisiana is literally at a crossroads,” Appel said. “We either move forward into the 21st century or go back where we have been, at the bottom of the heap.”

Follow Will Sentell on Twitter, @WillSentell. For more coverage of Louisiana government and politics, follow our Politics blog at http://blogs.theadvocate.com/politicsblog.