President Donald Trump’s campaign to politically punish Republicans who stand in his way moves through Indiana on Tuesday, when seven state senators face Trump-backed primary challengers.

In neighboring Ohio, primaries for U.S. Senate and governor will lock in the candidates for two major races with national implications.

And in Michigan, voters in a bellwether district will fill a vacancy in the state Senate, a race with implications for the balance of power in a battleground state.

Here’s what to watch for.

How strong is Trump’s grip on the Republican Party?

Trump is taking aim at seven Republican state senators in Indiana who opposed his plan to redraw congressional district boundaries to help the party gain seats in the U.S.…