The Democrats haven’t been popular with the military for a long time mainly because just about every effort the Democrats make is focused on removing benefits and weakening our military capability.
In nearly every election over the last forty years Democrats worked hard to disenfranchise the military vote in an attempt to increase their odds at winning. One of the better examples occurred during the 2000 election when the Democratic Party and the Al Gore election campaign attempted to have all the absentee votes coming from APO/FPO addresses thrown out of the vote. In some voting districts in Florida thousands of military absentee ballots were literally thrown in the trash before they were counted by democratic voting officials because they believed it would hurt Al Gore’s chances of getting elected. (Just a side note several studies have been done and it was concluded that if all the disputed votes had been given to Al Gore he would have still lost by over 500 votes)
Would you want to vote for a group that believes you have less right to vote if you’re out of your state serving your country than some unknown person that just shows up at the polling place… I know I wouldn’t.