I don’t think this is a good precedent, but it is possible that it is because of the chance of a major terrorist attack around the time of the elections. There have been a number of significant arrests and also strange events (sudden shut downs of Pakistan and British airports, for example) that make me think that there is something brewing. I don’t think the terrorists have a very good chance of pulling it off, but I suspect these units are going to be on hand just in case.
That is the reason we have a military after all, to protect the country against *foreign* threats to our security.