Former President Trump cruised to easy wins in five Republican presidential primaries Tuesday, and his candidate of choice in Ohio's crucial Senate race won — but once again, there were signs Trump has work to do in shoring up support in his party.

Why it matters: Trump, the only GOP candidate still running for president and the party's presumed nominee, once again saw a big percentage of Republican voters — almost 20% in most of Tuesday's contests — cast ballots for someone else.

• Most of those non-Trump votes in Ohio, Arizona, Florida, Kansas and Illinois went to former UN ambassador Nikki Haley, who suspended her campaign two weeks ago.
• The results were the latest warning signs that a sizable percentage of GOP voters may not show up for Trump in November, complicating his push to defeat President Biden.
• Biden easily won the Democratic primaries in Ohio, Illinois, Kansas and Arizona, posting larger margins than Trump did on the GOP side. Florida did not hold a Democratic primary.

Between the lines: Early exit polls Tuesday offered a reminder of the challenge Trump faces in uniting the GOP.

• 18% of Republican primary voters in Ohio said that they wouldn't support Trump in November, with 10% of those voters saying they prefer Biden, per ABC News' analysis of preliminary exit poll results.

Zoom in: Trump still flexed his influence within the GOP with wins for candidates he endorsed in down-ballot races.

• Chief among those was the Ohio Republican Senate primary, a contest at the center of the broader battle between MAGA and what remains of a GOP establishment. Trump endorsed Cleveland businessman Bernie Moreno, who was projected to win on Tuesday.
• Moreno will now take on Democratic Sen. Sherrod Brown in November, a contest that could go a long way toward determining which party controls the Senate next year.

Trump-backed state Rep. Derek Merrin was also projected to win in a competitive race in a northwest Ohio congressional district against former state legislator Craig Riedel.

• In California, Trump-endorsed state Rep. Vince Fong was heading for a May runoff in the special election to replace former House Speaker Kevin McCarthy (R-Calif.), AP projected.
• Fong, competing with eight other candidates, did not earn a majority of the vote to avoid a runoff. He'll likely face Tulare County Sheriff Mike Boudreaux (R) or Marisa Wood (D), a teacher.

Go deeper: Trump and Senate Democrats unite to boost Bernie Moreno in Ohio

Editor's note: This story was updated with additional details throughout.