With less than six weeks until the U.S. election, laws governing how Americans vote remain in flux in many battleground states, with the two parties locked in an intensive fight over the rules as President Donald Trump continues to suggest he will challenge any outcome unfavorable to him.

The combination of the pandemic, doubts about the capacity of the Postal Service to handle a flood of mail ballots and an aggressive push by Democrats to expand access to voting rights and counter Republican efforts to limit them has fueled litigation and legislative battles across the country that have not been resolved even as early voting has gotten underway.

The result is uncertainty that Trump is already seizing on in his extraordinary campaign to cast doubt on the election system and the result. In the latest of a string of remarks on the issue, the president refused Wednesday to commit to a peaceful transfer of power, igniting new concern about his commitment to the Constitution and drawing pushback Thursday from prominent members of his party.