Four years ago, a sitting president — rejected by American voters — attempted to seize a second term anyway, plunging the nation into confusion, conflict and, in its last gasp, violence.

Now, Donald Trump’s political comeback has revived a sense of dread among the officials and institutions who stood in his way last time: Could it happen again?

Dozens of interviews with people deeply familiar or involved with the election process point to a clear consensus: Not only could Trump make a second attempt at overturning an election he loses, he and his allies are already laying the groundwork.