The decision this week by MNsure's top-selling insurance company to withdraw from the state exchange injected Minnesota's health care exchange efforts back into the political debate as the November election nears.

Republican gubernatorial candidate Jeff Johnson sharply criticized Gov. Mark Dayton on Thursday over his management of MNsure, using its struggles as a means of questioning the incumbent DFLer's competence on the job. Dayton has repeatedly apologized for the troubled launch of MNsure, but has talked up its benefits while charging that Johnson "doesn't know what he's talking about" on the issue.

The federal Affordable Care Act inspired one of the most bitter political debates of the past five years, and its ramifications continue to play out in both national and Minnesota politics. Johnson and other Republicans pounced at the news that PreferredOne would pull its policies from MNsure in advance of November's open enrollment.

On Thursday, Johnson held his second news conference about MNsure in two days; he planned a third for Friday. At a Minneapolis engineering company, Johnson criticized Dayton's decision last year to deny a waiver to small businesses not in compliance with the health care law because they do not meet mandated coverage requirements.

At Mack Engineering, which manufactures machined components for companies like John Deere and Honeywell, co-owner Jennifer Salisbury said her 28-employee company's health insurance premiums had skyrocketed. The company's small group insurance plan is not in compliance with the Affordable Care Act. The Obama administration offered states more time to get small group plans in compliance, but Minnesota declined.

"This is another example of Gov. Dayton hurting small businesses and their employees," Johnson said. "He wouldn't stand up for the Mack Engineerings of Minnesota."

Dayton, speaking to reporters after attending an event at Best Buy headquarters in Richfield, charged that Johnson doesn't understand the issue. He noted that according to a Department of Commerce survey, about 75 percent of Minnesota companies are ACA-compliant. Exempting those that aren't would raise rates for those companies that are compliant, Dayton said, while also leaving employees at noncompliant companies with insurance coverage that's subpar under the terms of the federal health care law.

Plans that comply with federal mandates "are going to be far more comprehensive than what they were offering before," Dayton said. One of the major goals of the ACA, Dayton said, "is to get everybody up to at least a good standard and hopefully an even better one."

Under Dayton, Minnesota was among one of the most active states in implementing the provisions of the ACA. The ensuing struggles of MNsure, primarily a glitch-laden website that's still not 100 percent functional, left already-critical Republicans plenty of fodder with which to criticize Dayton and DFL legislators.

The issue had receded somewhat amid slowly rising insurance coverage rates; Minnesota's rate of people without insurance recently dropped below 5 percent. But this week's news about Golden Valley-based PreferredOne gave Republicans another chance to make MNsure an issue.

PreferredOne had set the lowest premium prices in the nation last year, and signed up nearly 60 percent of MNsure consumers.

MNsure leaders characterized the PreferredOne decision as part of the expected evolution of what's meant to be a competitive marketplace. The state Department of Commerce is planning to release insurance rates and the names of insurers selling 2015 coverage on the site early next month.

A Star Tribune Minnesota Poll of 800 likely voters, taken earlier this month, found a dim view of MNsure's efforts so far. Forty-four percent of respondents called MNsure "mostly a failure," while 33 percent considered it a success.

Still, a growing number of Democrats have shown a willingness to tout the successes of the Affordable Care Act.

"Minnesota's uninsured rate has dropped below 5 percent, and we hear stories every day of people who weren't able to get coverage before that are paying low premiums for quality coverage now," Mike Obermueller, the DFL-endorsed opponent to Republican U.S. Rep. John Kline, said Thursday.

Dayton said he believes the health law's supporters, starting with the Obama administration itself, have been too reluctant to champion it.

"The experience that people have is ultimately going to prevail," Dayton said.

Patrick Condon • 651-925-5049