COLUMBUS, Indiana — Elections in the US states of Indiana, Michigan and Ohio on Tuesday made a picture increasingly clear — that President Donald Trump still dominates the Republican Party, and Democrats seem to have the momentum ahead of November's midterm elections.

The biggest test of the president's power came in Indiana, where he backed primary challenges against seven Republican state senators who rejected his redistricting plan in December. Five of the president's candidates won.

"Big night for MAGA in Indiana," US Senator Jim Banks wrote on social media, adding that he was "proud to have helped elect more conservative Republicans to the Indiana State Senate".

It's been a costly and unprecedented intraparty battle that has exacerbated tensions among Republicans ahead of the November midterm elections that will determine control of Congress.

State Senator Travis Holdman, one of the incumbents to lose his primary, said he was at peace with his defeat. He voted against redistricting and faced more than $1.3 million in attack advertising funded by organizations tied to Banks and Governor Mike Braun.

"I did what my constituents asked me to do and it cost me my job," he says. "But that's OK."

Holdman warned that a more aggressive style of campaigning was arriving in his state.

"Welcome to DC politics in Indiana because this means that's what's coming," he said.

The race that was too close to call was the most expensive of the seven primaries.

The fundraising groups led by Banks and Braun combined to spend more than $2.2 million on advertising attacking Senator Spencer Deery, according to the ad-tracking firm AdImpact.

Trump began leaning on Republican-led states last year to redraw their congressional maps to make it easier for his party to hold its thin majority in the US House. Although redistricting is normally done once a decade, after a new census, the president wanted to abandon tradition to gain a political edge.

Texas was the first to follow through, and the White House pressured Indiana to go along, too. Vice-President JD Vance met with state politicians in Washington and Indianapolis, and Trump weighed in by conference call.

Meanwhile, in Michigan, Democrat Chedrick Greene won a special election on Tuesday, securing the party's control of the state Senate through the remainder of Governor Gretchen Whitmer's term.

Over in Ohio, primaries locked in candidates for two major races with national implications.

Agencies via Xinhua