Trump has the support of 40 per cent of the Republican primary voters and is followed closely by Senator Ted Cruz with 35 per cent and Ohio Governor John Kasich with 24 per cent, according to a latest opinion poll by NBC News and The Wall Street Journal.
Meanwhile, in the Democratic party, Sanders (46. 3 per cent) has all but eliminated Clinton's (47.7 per cent) primary polling lead, it said.
"As she is finishing this primary, she is not gaining strength. The cracks are showing, and she is losing strength," said Bill McInturff, a Republican pollster who conducted the survey with Democrat Fred Yang.
However, in a hypothetical match-up Clinton defeats Trump with 50 per cent to 39 per cent.
