Donald Trump and rival Ted Cruz have traded harsh personal attacks as Indiana voters picked which candidate they want to be the Republican presidential nominee.

Exit polls are due out imminently in the Hoosier state’s primary, with Mr Trump tipped to deal a potential death blow to the Texas senator‘s White House hopes.

On Tuesday morning, the real estate baron tried to link Mr Cruz’s father to Lee Harvey Oswald, the alleged assassin of President John F Kennedy.

Speaking to Fox News, Mr Trump cited an unsubstantiated National Enquirer story claiming that Rafael Cruz had appeared in a 1963 photo alongside Oswald in New Orleans.

U.S. Republican presidential candidate Ted Cruz speaks with supporters of fellow candidate Donald Trump at a campaign event outside The Mill in Marion, Indiana

Indiana could be Ted Cruz’s last stand

Mr Cruz hit back, saying of his rival: “This man is a pathological liar.

“He doesn’t know the difference between truth and lies. He lies practically every word that comes out of this mouth.”

Mr Cruz also called the businessman “amoral”, a “serial philanderer” and warned the country could “plunge into the abyss” if he becomes president.

In the Democratic race, Vermont Senator Bernie Sanders is hoping for victory over Hillary Clinton.

However, even if he does win it would be was unlikely to slow her march to that party’s nomination.

Mr Cruz has staked everything on winning Tuesday’s primary in the mid-western evangelical heartland of Indiana.

But polls show he might come up short against Mr Trump again – and even big supporters say that might doom his campaign.

Victory for Mr Cruz might set him up for a scrap for delegate votes with Mr Trump at the party’s convention in Cleveland in July.

No one really knows what that would look like, how it would work or how Mr Trump would react to being robbed of the nomination by the party machine.

The billionaire continues to dominate the race and believes he is now what he terms the “presumptive nominee”.

Mr Cruz’s campaign has generally fared better in states with a high proportion of voters who identify as evangelical. They are often wary of Trump.

His supporters hope victory in Indiana could be a springboard to generate donors and support in California, the giant prize which will vote next month.

Mr Cruz appears determined to stay in until Cleveland and fight until the last – defeat in Indiana might make the pressure intolerable.