Gov. Mark Dayton signed it into law Wednesday, enacting the most sweeping health care change the state has seen in half a century. Some 1.3 million Minnesotans and small businesses are expected to buy their health coverage through the exchange, starting next year, including 300,000 who are now uninsured.

The governor was flanked by dozens of DFL lawmakers at the bill signing and not one Republican, a sign of the ferocious partisan battles that marked the exchange’s two-month journey through the DFL-controlled Legislature.

“It’s unfortunate that how we can best provide health care to all the people of Minnesota has become such a starkly partisan, really ugly matter for the last year,” Dayton said. “But I think the people of Minnesota, the people of this country have spoken. They want better quality health care. They want it at lower cost.”

Republicans, meanwhile, were already coming up with alternate names for the new exchange — including M-unsure and MNdoubt.

“This was ugly politics created by the DFL,” said Senate Minority Leader David Hann, R-Eden Prairie, whose members staged an almost 12-hour debate on the exchange last week. He predicted the exchange “is going to be very, very poorly received by the public. It’s not going to accomplish what they say they were going to accomplish. I think they are going to be in for a big surprise.”

State-based exchanges like MNsure are key to the federal Affordable Care Act. By 2014 health insurance will be mandatory for all Americans, and exchanges are supposed to be one way for the uninsured, the underinsured and the self-insured — both individuals and small businesses — to easily comparison-shop for the best plan at the best price.

But the sheer scope and cost of the health insurance exchange alarmed critics in the Legislature, the business community and the insurance industry.

Republicans fought to limit the power of the seven-member MNsure board, which will have the authority to pick and choose the plans that will go into the marketplace, starting in 2015. They also questioned the exchange’s $64 million annual budget, its ability to safeguard users’ data privacy, and even whether the state can really get the massive system up and running in time to start enrolling its first customers on Oct. 1.

Its supporters, however, say it will drive down health costs for health care providers — who won’t have to shoulder millions of dollars in uncompensated health care coverage for the uninsured — and for exchange participants who may qualify for federal tax credits if they enroll.

“This is the most significant reform of health insurance we have seen in 50 years,” said Rep. Joe Atkins, DFL-Inver Grove Heights, who sponsored the House version of the exchange bill. “It’s not simply significant because you can purchase your health insurance from a website and have that convenience.”

Atkins joked that he’d had dental surgery the morning of the bill signing without numbing Novocain and “it was actually a little less painful” than the two and a half months it took to push the exchange bill through 18 committees, more than 70 hours of testimony and a series of House and Senate floor debates that stretched long into the night.

MNsure passed without a single Republican vote in favor, but Atkins credited his GOP colleagues with crafting large parts of the final legislation.

“They did great work,” Atkins said, singling out GOP pushes to ensure that the new health insurance marketplace will have tough oversight and will safeguard users’ personal data. “I still want to thank them, whether they voted for it or not.”

In the coming months, the state will scramble to set up the technology infrastructure for the new exchange, name the new board’s members, get health plans lined up to sell and spread the word to Minnesotans about how the new exchange will work.

“This is a great day for the people of Minnesota,” Dayton said after signing the bill. “This is a day we’re taking a major step forward to improve the quality of health care, the affordability of health care and to put the people of Minnesota and their interests in charge of our health care system.”