Theresa May made the 2017 election about Brexit, look what happened. Labour’s Brexit policy was totally flawed and lacked coherence: access to single market, but ending freedom of movement wasn’t going to happen. It didn’t matter because they weren’t going to win, and needed to appease their metropolitan city voters and their working-class constituencies that voted leave.
I weren’t born then, but Ted Heath also framed the 1974 election over a single issue and lost that election. Generally, it’s not a good idea to have an election over a single issue.