In the Trump era, it’s rare to see a GOP leader in Congress publicly disagree with President Trump on an issue of great importance to the president.

But that’s what happened this week when Sen. John Thune of South Dakota – the second highest-ranking Republican in the Senate – pushed back when questioned about Trump’s monthslong crusade against expanding voting by mail.

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Asked if he agreed with the president’s repeated charges that mailed-in balloting will lead to a “rigged election” and “massive voter fraud,” the Senate majority whip told reporters, “I don’t.”

“Mailed-in voting has been used in a lot of places for a long time and, honestly, we’ve got a lot of folks that, as you know, they're investing heavily in trying ... to win that war. It's always a war too for mail-in ballots. Both sides compete, and it's always an area where I think our side, at least in my experience, has done pretty well,” Thune answered, adding: “I think we want to assure people it's going to work, it's secure and if they vote that way it's going to count.”

Thune isn’t the only Republican airing concerns about the president’s full-court press against voting by mail, amid worries that the charges could depress Republican turnout in the November general election, when the GOP will be defending the White House as well as the party’s 53-47 majority in the Senate.

Sen. Marco Rubio of Florida also disagreed with the president’s strategy. On a Trump reelection campaign conference call last weekend to discredit potential Joe Biden running mate candidate Rep. Karen Bass, Rubio was questioned about Trump’s stance.

“No, I'm not concerned about mail-in voting in Florida," the senator briefly answered.

With 29 electoral votes up for grabs in the presidential election, Florida has long been the biggest of the battleground states in the race for the White House.

Both the president and the presumptive Democratic nominee are pouring money and resources into a state that Trump narrowly captured four years ago. An average of the latest public opinion surveys in the Sunshine State compiled by Real Clear Politics shows that the former vice president holds a 6-point advantage over the GOP incumbent in the White House.

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Amid the tensions in the party over the issue, the president earlier this week made an about-face in his charge against voting by mail – at least in Florida’s case.

“Whether you call it Vote by Mail or Absentee Voting, in Florida the election system is Safe and Secure, Tried and True. Florida’s Voting system has been cleaned up (we defeated Democrats attempts at change), so in Florida I encourage all to request a Ballot & Vote by Mail!,” the president tweeted.

That was a big switch coming from a president who for five months has blasted attempts to increase mail-in balloting amid health concerns of in-person voting during the coronavirus pandemic.

“Republicans should fight very hard when it comes to state wide mail-in voting. Democrats are clamoring for it. Tremendous potential for voter fraud, and for whatever reason, doesn’t work out well for Republicans,” Trump argued in early April.

A month later he claimed, “The United States cannot have all Mail In Ballots. It will be the greatest Rigged Election in history. People grab them from mailboxes, print thousands of forgeries and 'force' people to sign. Also, forge names. Some absentee OK, when necessary. Trying to use Covid for this Scam!”

The president’s change of course in the Sunshine State came as Florida’s Secretary of State’s office reported that, while Republicans have closed the voter registration gap with Democrats, Democrats have a massive 500,000 advantage in supporters who’ve signed up to vote by mail.

The president pointed to Florida’s current GOP governor – a major Trump supporter – as well as his Republican predecessor in Tallahassee in explaining his turnabout.

“They’ve been doing this over many years and they’ve made it really terrific,” he told reporters.

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At the White House on Monday, Trump distinguished between universal mail-in ballots and absentee balloting.

"Absentee ballots are great," Trump clarified. "They go through a process. You have to request them. But the universal mail-in ballots have turned out to be a disaster."

But some election officials argue there’s little effective difference between absentee voting and voting by mail. Five states voted entirely by mail even before the pandemic. They are Washington state, Oregon, Colorado, Utah and Hawaii. Amid the coronavirus, many states with both Democratic and Republican governors have moved to make it easier for voters to send in ballots by mail. And in June, Democratic Gov. Gavin Newsom of California signed into law a measure that requires his state to send every registered voter a ballot. Vermont is doing the same.

This week, Nevada’s Democratic governor signed into law a bill that sends ballots to all registered voters in year’s general election. The Trump campaign, the Republican National Committee, and the state GOP immediately filed a suit against Nevada over the new law, claiming that the measure will undermine the election’s “integrity.”

Election experts do say that voting by mail is more susceptible to fraud than casting a ballot in person, but they’ve seen no evidence of widespread fraud or that absentee balloting favors Democrats. But the massive increase in absentee balloting places an extra burden on already stressed-out state and county election officials and on a U.S. Postal Service facing financial and manpower deficits.

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Regardless of his about-face in Florida, some Republicans remain concerned that the president’s rhetoric on voting by mail will come back to bite the GOP this autumn.

Former Rep. Zach Wamp, a conservative from Tennessee who’s working with the election advocacy group Issue One to push for Congress to approve more election security funding, told Fox News he’s “concerned that the president may be unintentionally suppressing the very voters who are most upset with the mob and the socialist agenda.   They typically are more conservative which means they like to be careful in how they vote. Obvious to me. Surely he trusts the states he won in 2016 with carrying out the election how they see fit including absentee voting.”

And retweeting the president, Wamp – who was a Trump critic during the 2016 election – emphasized “Mr. President sir !Lots of red states (+blue states) need $ to carry out early voting expansion +legitimate absentee voting. GOP needs all seniors to vote. With extra pressure, the states need $ now.”

Former Massachusetts Gov. Bill Weld, who last year launched a long-shot unsuccessful primary challenge against the president, told Fox News that Trump’s attacks on voting by mail “will suppress Republican turnout in battleground states.”

Pointing to the voting by mail registration in Florida, Weld argued that “Trump can’t afford to give up such a margin in who’s going to be voting by mail.”

But longtime Republican consultant John Brabender – a veteran of multiple Republican presidential campaigns – said that when it comes to dealing with the Democrats, “I think the president has decided that we’re going to beat them at their game and I’ve seen a fundamental shift in the past three weeks where Republicans have started to light a fire and say ‘it’s game on’ and they're saying ‘we’re not going to just sit back and watch this happen and simply complain about it. We’re now going to fight them at their own game.’”

Brabender emphasized that “if this is the system that we have to play under, then that’s the system that we have to win under. The Trump campaign is now engaged on this and making great progress on this and we can’t be dependent on Democratic judges to do the right thing in a lot of cases.”