It means that whoever said or wrote that expects, that at a forthcoming election or any vote where the losers will no longer have any say, will loose the vote. Like when a party losses an election and they no longer govern. The person saying it is on the opposing side and is expecting their side to win the vote or election.

Some positions, such as elected officials, are voted for by people, in some sort of ballot, collection of opinions, usually on paper and voting centres. Examples: mayors and government positions in some societies. Officers, such as Chairman, president, of some society, group, or club. The guys who is to get the pizza for your bowling team. We all vote that Harry gets the pizza. The people who are elected, usually those who receive the most votes, are "voted in". voted into those positions. If you hold one of these positions, that is, have been voted in, in the past and the next election, the next time people vote, you do not win, you have been "voted out": you are out of that position. . We will vote you out. We, a group pf people, allowed to vote, will vote for someone else and not for you, so that you will lose you position.