One of the major storylines emerging from Republican and Democratic primary races in the United States is the influence that women are exerting on the electoral fortunes of leading candidates.

While Donald Trump has established himself as the most popular candidate in the Republican nomination battle, his formula for dominating primary races in the last month has also come at a price.

Mr Trump’s bombastic and aggressive style is winning over male voters in spades across most states, but not women.

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A “gender discount” worth around 5 to 10 per cent was again evident in his electoral performances in the five bellwether primaries held on Wednesday (Australian time).

According to CNN exit polls, Mr Trump’s loss in Ohio was partly attributable to the gender discount in his overall vote.

Although 39 per cent of male Republicans in the state backed the billionaire, his aggregate share of the vote was much lower because only 33 per cent of women supported him.

Mr Trump claimed an easy victory in Florida after capturing a massive 52 per cent of the male vote. However, the gender discount was also apparent in that state with only 40 per cent of women voting for him.

This trend was also evident in the Republican contests in Missouri, Illinois and North Carolina – all of which Mr Trump won.

Mr Trump is dominant in the Republican race partly because more men than women are participating in each of the state primaries.

A majority of female voters are on Hillary’s side. Photo: AP

However, the Democratic race between Hillary Clinton and Bernie Sanders is being fought on contrasting terms.

Mrs Clinton’s thumping wins in Florida, North Carolina and Ohio were partly attributable to the overwhelming support she won from female voters.

In Florida, Mrs Clinton wiped the floor with 66 per cent of the total vote.

Almost 70 per cent of women who voted in that contest supported her, compared to around 59 per cent of men.

The importance of the female vote was magnified because more women participated in the Democratic vote in Florida than men.

A contest between Mr Trump and Mrs Clinton for the presidency could be determined by gender politics.

It might boil down to whether the number of Republican women now disaffected with Mr Trump would outweigh a potential exodus of Democrat-leaning male voters from Mrs Clinton.

Only the November election can settle that poser, although Mr Trump has already demonstrated that he can attract votes from blue-collar male workers in traditional Democratic states such as Michigan, with his promises to raise wages.

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John Kasich has plenty of fans. Photo: AP

Even though Mrs Clinton and Mr Trump are the clear frontrunners to secure the nominations of their parties, each of their campaigns could still implode.

Uncertainty surrounds the outcome of an FBI investigation into Mrs Clinton’s use of a private computer to send emails when she was Secretary of State in President Barack Obama’s first administration.

The FBI is investigating whether she breached security laws.

Mr Trump will likely finish the primaries in June with the most delegates of the three candidates still in the Republican primary race, but he faces a likely challenge from Ohio Governor John Kasich if he is unable to secure an outright majority.

Mr Kasich could win the Republican nomination if he can muster support from delegates who were bound to candidates such as Marco Rubio and Jeb Bush, who have both abandoned their campaigns.