Gov. Nathan Deal faces the biggest test of his second term Tuesday when voters decide the fate of his failing schools initiative, and the outcome will shape his final years in office.

The constitutional amendment, which would allow the state to take control of persistently struggling schools, was the most concrete promise that emerged from his 2014 re-election campaign and his top priority in his final years in public office.

A defeat could force him to scale back the remainder of his second-term agenda, including his vision to overhaul school financing, and pursue alternatives that give the state other, perhaps less-controversial, options to intervene in troubled schools.

With polls showing Amendment 1 in trouble, Deal said Sunday he's prepared to come up with a Plan B.

“I’m hopeful that it’s going to pass. But I’m not going to give up on trying to help children that are in these chronically failing schools,” Deal told our AJC colleague Tamar Hallerman over the weekend. “Our state can’t afford to lose that many children and their futures.”

Deal and his allies still have favorable ballot language on their side, plus millions of dollars in advertisements urging for its passage. The governor pitches it as a way to save thousands of students he says are "trapped" in failing schools, and he warns that many will go on to a life of crime and violence.

But teachers groups and other opponents have spent more than $5 million to oppose the plan and polls show strong resistance from both Democrats and Republicans. Conservative critics say it defies the sacred right of local control and left-leaning opponents see it as a power grab.

If the measure is scuttled, Deal’s critics will be eager to paint him as an ineffective lame duck, hobbled by solid opposition from Democrats but also rear-guard attacks from Republicans who are still smarting over his vetoes of the “religious liberty” and “campus carry” measures.

And the governor and his allies will cast it as a smear effort by deep-pocketed education groups. They’ll be quick to remind those who seek to dismiss him that he has the first and last say over the state’s budget, a trove of additional appointments at his disposal and, of course, his veto power.

He’ll also probably spend much of his remaining political capital on finding another alternative to the Opportunity School District - one that might not need a statewide vote.

“We’re going to look at everything that’s possible,” he told Hallerman when she asked if there’s another path if the amendment fails.

He added: "I’m going to continue to do everything I can to make sure we close that gap of educational opportunity.”