LANSING, Mich. — Republican Donald Trump and Democrat Hillary Clinton looked to pad their leads in Tuesday's primary contests in Michigan and Mississippi, eager to turn their attention toward a general election fight for the White House.
Trump is facing a barrage of criticism from rival candidates and outside groups desperate to block him from becoming the Republican nominee. While the real estate mogul holds a solid lead in the delegate count, his recent losses to Texas Sen. Ted Cruz have raised questions about his durability and have given fresh hope to other competitors.
Ohio Gov. John Kasich tried to mount a strong challenge to Trump in Michigan, Tuesday's biggest delegate prize. Kasich has yet to win a primary but hoped a good showing in Michigan would give him a boost heading into next week's crucial contest in his neighbouring home state.
Speaking to a crowd in Lansing, Kasich said a strong showing in Michigan would show the country "that it's a new day in this presidential campaign."
To that end, Kasich and Florida Sen. Marco Rubio were using recorded phone calls from Mitt Romney to appeal to voters as they headed to the polls. Romney, the 2012 Republican standard-bearer, has not endorsed a candidate but has vowed to help challengers to Trump, who he says would be dangerous for the country.
Idaho and Hawaii also held Republican contests.
At stake Tuesday were 150 delegates for the Republicans and 179 for Democrats.
Clinton entered Tuesday's primaries with the Democratic nomination in sight. After a shaky start in early voting states, she's pulled off commanding wins in states with large black populations, showcasing the limits of rival and Vermont Sen. Bernie Sanders' appeal.
Sanders is strong with young people and white, blue-collar voters, drawn to his calls for free college tuition and breaking up Wall Street banks.
Michigan, with big college towns and a sizeable population of working-class voters, should be a good fit for Sanders. But Clinton has led in polling.
Tuesday's contests are a prelude to next week's high-stakes primaries in Florida and Ohio. Like Ohio's Kasich, Marco Rubio must win his home state in order to remain a viable contender.
Rubio has received endorsements from a steady stream of senators, governors and other high-profile Republican officials. But his backing from voters has lagged, and he entered Tuesday's contests with just a pair of victories in the Minnesota caucuses and Saturday's Puerto Rico primary.
If Rubio and Kasich can't win at home, the Republican primary looks to become a two-person race between Trump and Cruz. The Texas senator is sticking close to Trump in the delegate count and with victories in six states, he's arguing he's the only candidate standing between the brash billionaire and the nomination.
Some mainstream Republicans have cast both Trump and Cruz as unelectable in a November face-off with the Democratic nominee. But they're quickly running out of options and are increasingly weighing long-shot ideas such as a contested convention or rallying around a yet-to-be-determined third-party candidate.
Heading into Tuesday, Trump led the Republican field with 384 delegates, followed by Cruz with 300, Rubio with 151 and Kasich with 37. Winning the Republican nomination requires 1,237 delegates.
Among Democrats, Clinton had accumulated 1,134 delegates and Sanders 499, including superdelegates. Democrats need 2,383 delegates to win the nomination.