CLEVELAND, United States (AFP) — Five major American states vote tomorrow in a crucial test for the White House race, with Donald Trump hoping to lock in the Republican nomination despite a barrage of attacks over his firebrand tactics.

Dubbed “Super Tuesday 2” by US media, the latest key date of the November 2016 election cycle will see Democratic and Republican contests in the states of Florida, Ohio, Illinois, Missouri and North Carolina.

The first three states are winner-take-all in terms of delegates for the Republican race, the first such contests of the primary season and a major prize as the front-runner Trump seeks to propel himself towards the 1,237-delegate majority needed to secure the party nomination.

Just as the billionaire was striving to adopt a more presidential tone, the tensions surrounding his high-octane rallies, the target of systematic protests by activists angered by his anti-immigrant rhetoric have exploded into violence, and thrown the race into turmoil.

Trump forged ahead on the campaign trail through the weekend after calling off a rally in Chicago amid scenes of chaos on Friday. The following day in Ohio brought a fresh security scare as a protester tried to rush on stage towards the candidate.

For the Republicans the stakes could not be higher, with the day expected to further winnow the field down from the current four contenders: Trump, Texas Senator Ted Cruz, Florida Senator Marco Rubio and Ohio Governor John Kasich.

With Kasich and Rubio both facing make-or-break tests in their home states, both have embarked on a bout of frenzied campaigning.

Trump holds a two-digit lead over Rubio in Florida, but Kasich currently beats the billionaire by a whisker in Ohio according to the RealClearPolitics average of polls. A defeat on home turf is likely to be a kiss of death for Kasich, who holds last place in the Republican primaries.

A visibly unsettled Rubio who was seen as the Republican establishment’s best chance to beat Trump but has disappointed in the race so far has said that keeping his word about supporting Trump if he wins “is getting harder every day”.

Cruz, an ultra-conservative with links to the Tea Party movement and a champion of the religious right, is polling in second place nationally and believes a victory over Trump would be within reach if the race were whittled down to two.

To date, Trump has 462 delegates, leading Cruz who has 371, Rubio with 165 and Kasich with 63.