The governor of Washington state in the north-western United States has activated some members of the National Guard to be on stand-by in case of election-related unrest.

A ballot drop box for early voting was set on fire with flammable devices in Vancouver at the start of the week; Hundreds of ballots were destroyed, and a similar incident occurred in nearby city of Portland, Oregon around the same time.

A statement from Governor Jay Inslee’s office whichsays the move is a “purely precautionary measure,” said the guard will be on stand-by for four days in Washington state, beginning Monday, and ending just after midnight on Thursday.

Election Day is tomorrow Tuesday but tens of millions of early votes have already been cast.