While such last-minute changes are highly unusual, states have broad autonomy to define the timing and procedures for primary elections. The exact process for setting primary dates varies from state to state. That is why a number of states changed the dates of their primaries and caucuses between 2016 and 2020, and why Republicans in several states were able to cancel their 2020 primary elections to minimize intraparty competition for President Trump.

But the Democratic Party also has its own rules requiring that all primary elections be completed by June 9, and that all delegates to its national convention in Milwaukee be selected by June 20. Any states that defy that timetable — including Louisiana — could be penalized by the national party with a reduction in their delegate count.

Could the general election be postponed or canceled?

Only with enormous difficulty.

The date of the general election is set by federal law and has been fixed since 1845. It would take a change in federal law to move that date. That would mean legislation enacted by Congress, signed by the president and subject to challenge in the courts.

To call that unlikely would be an understatement.

And even if all of that happened, there would not be much flexibility in choosing an alternate election date: The Constitution mandates that the new Congress must be sworn in on Jan. 3, and that the new president’s term must begin on Jan. 20. Those dates cannot be changed just by the passage of normal legislation.

After Louisiana’s announcement on Friday, Marc Elias, the prominent Democratic election lawyer, knocked down what he described as a wave of queries about whether the November election could be similarly revised.

“I am getting a lot of questions about the November election,” Mr. Elias wrote on Twitter. “While states can set their own primary days, the federal general election is set by federal statute as the the [sic] Tuesday following the first Monday in November. This date cannot be changed by a state nor by the President.”