WASHINGTON (BLOOMBERG) - Republican efforts to roll back virus-fighting measures have been steaming ahead for months, and little could halt their momentum Friday (Oct 2) even as President Donald Trump became one of more than 30,000 Americans hospitalised with Covid-19.

In Michigan, the state Supreme Court invalidated dozens of Governor Gretchen Whitmer's pandemic executive orders.

In Wisconsin, Republican legislators filed a brief in support of an effort to block a mask requirement amid one of America's most dire outbreaks.

And in Mississippi, Governor Tate Reeves defended his move this week to end his own mandate, the first such move in the US.

But the political moment was newly uncertain as information about the president dribbled out of the White House: mild symptoms in the morning, an experimental medicine in the afternoon and a helicopter flight to Walter Reed National Military Medical Centre in the evening.

Rank-and-file Republicans and officials spoke more tentatively about measures to curb the pandemic than they had in months. Where they once were strident, on Friday they explained, excused and warned.

In June, Montana state Senator Fred Thomas had called masks "a hoax to push government compliance."

On Friday, he said in an email that "there are a million ways to catch this or transfer this virus," mask or no mask, and that "we all need to continue to be vigilant in protecting the vulnerable."

"We need to be very cautious and careful!" he wrote.

The news quelled some fractious corners of the party.

For months, Ohio Governor Mike DeWine, a Republican, has been denounced by the far-right fringe of his own party.

Fellow Republicans backed legislation to roll back his executive powers and impeach him, and one lawmaker even sought criminal charges against him for "terrorism."

But the normally active Twitter and Facebook accounts of some of his harshest critics went silent after Trump's diagnosis.

DeWine frequently tells reporters when he receives blowback from the right. On Friday, he said he hadn't received a single critical message.

Trump's illness came after he had frequently mocked mask-wearers and tried to undermine state and local rules meant to stem the pandemic.

Local officials had followed his lead, and on Friday gambits set in motion weeks ago continued to play out.

Michigan's highest court found dozens of Whitmer's actions unconstitutional.

In a 4-3 ruling by its Republican majority, the court found that a 1945 statute allowing governors to make executive orders on public health delegated too much power to the office.

The ruling invalidates orders including business restrictions and mask mandates, and will require Whitmer to compromise with Republicans on any health emergency orders that extend beyond 28 days.

"With this decision, Michigan will become the sole outlier at a time when the Upper Peninsula is experiencing rates of Covid infection not seen in our state since April," Whitmer said in a statement.

While legal challenges have been launched across the country in response to gubernatorial actions to the pandemic, Whitmer was the first governor to have her emergency executive authority eviscerated.

President, Citizen In Pennsylvania, Republicans have been battling to strip Democratic Governor Tom Wolf of emergency powers, which he has used since March to manage shutdowns and issue a statewide mask-wearing mandate.

After failing to override the governor's veto and losing before the state Supreme Court in July, Republicans are taking their bill to limit Wolf's powers to a ballot initiative that could come before voters as soon as May.

Republicans believe that the peak of the pandemic has passed and, because hospitals aren't overwhelmed, people shouldn't have to follow strict orders, said state Representative Russ Diamond, who sponsored the original bill to check Wolf's powers. Trump's diagnosis hasn't deterred him.

"It really only changes the view of the issue if he gets really sick. But if he gets really sick, the guy's overweight, probably has some blood pressure issues, you always have to take those things as a factor," said Diamond.

"Even though he's the president, he's still one individual, and you can never make a judgement for an entire society based on one individual case."

Diamond himself is in quarantine after exposure to a fellow lawmaker who tested positive.

Big Country Medical experts have said masks are among the surest ways to discourage infections, but Trump has rarely appeared in public wearing one, and they have been rare among staffers in the West Wing's tightly packed offices.

Still, party members said the president's infection could have happened to anyone.

"You can't wear a mask every time you talk," said Cynthia Cole, chair of the King County Republican Party in Washington state.

"I wasn't 100 per cent surprised."

The White House outbreak has reached the top echelons of the Republican Party, lawmakers and donors, but Cole said Trump's policies aren't to blame for endangering people.

"He's taking a holistic approach," she said. "You've got to consider everybody, and that's hard to do. We've got a huge country."

Gritting It Out Some Republicans expressed fatalism and continued to deny the power of the virus, which has killed almost 209,000 Americans.

Mitchell Tracy, a 57-year-old former auto claims adjuster from Las Vegas, said his support for Trump was unshaken.

"I feel real sad that they got it, but I think everything's a joke," said Tracy, who retired early in 2018 and went on disability for a heart condition.

He said Trump is in better shape than he is.

"If I was him I would be cavalier, too," said Tracy.

"I think he's showing power, strength, not being fearful. He's a strong leader; he's not showing weakness."

James Buchal, party chairman in Multnomah County, Oregon, denied scientific studies showing masks cut down on viral transmission.

"It's speculation to say that him wearing a mask or not would have made any difference," Buchal said.

But in Washington, Cole said she had told canvassers to wear them: "I said, 'This is a matter of being polite and considering other people's feelings.'"

For months, the Covid-19 pandemic has surged sequentially around the nation, from the Pacific Northwest to the Northeast, then the Deep South and Sun Belt.

Now there are record daily cases reported in Montana and South Dakota, and Wisconsin has become a hot spot.

On Friday, however, Mississippi's Tate said there was little danger in lifting the state's mask mandate.

"Wearing a mask and staying socially distanced helps," he told Y'all Politics, a website that covers the state's politics. But, he said, the virus had retreated meaningfully in his state.

"Many on the left have overplayed their hand," Tate said.

"I think that they are using this in the election, because if we were talking about the economy, President Trump wins."

Hugh Reed, a Republican and top elected administrator for Armstrong County, Texas, said in an interview that Trump's diagnosis won't change his stance.

Armstrong - southeast of Amarillo, where meatpacking plants were the site of severe outbreaks - opted out of Texas Governor Greg Abbott's mask order because of its small population and few cases.

"I don't feel bad for the president at all," he said.

"I can't imagine a better way to spend 14 days of quarantine than with that gorgeous wife he's got."

Melania Trump remained in the White House as the president was choppered to Walter Reed on Friday evening.