It's very difficult to find senate candidates and this is why Half of the current senate delegations don't vote when there is an amendment. One third maybe participates in the senate discussion.
Let's create for additional vacancies, given how active this game is, I'm sure this is going to bode well!!!
The one thing you left out here is that that half is almost solely Labor.
And the "totalitarian option has been used before", by your party
You state a problem that frankly is a partisan problem and not an overall problem for the game.
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I don't get why it is a big deal, it will have to pass in a referendum in february anyways, which people can nay vote for. And even if that passes, Fremont and Lincoln will overall still be dominated by center-of-left parties, and so will Atlasia at large if your party bothered to turn out for once, which they will if Pericles does the GOTV.
Make an argument why you need to get elected, appeal to the swing voters and you are elected for a newly elected two term.
If not, there are plenty of options either and the Federalists are in no position to push anyone through for four of the five seats (and neither is your party at this point). In RL vacancies are filled sometimes with some bipartisan consensus (or used to like 20-30 years ago), or lean moderate/centrist to appeal to more.