Clinton, however, suffered an upset defeat at the hands of Bernie Sanders in Indiana but the outcome was unlikely to slow the 68-year-old former secretary of state's march to the Democratic nomination.
By becoming the presumptive nominee, Trump, who joined politics only last year, has scripted history as he is now on course to be the first standard-bearer of the party since Dwight D Eisenhower, a five-star general and the commander of Allied Forces in Europe during World War II, who had not served in an elected office.
Trump won 51 of the 57 delegates at stake in Indiana and now has 1,047 delegates in his kitty.
He is just short of 190 delegates, which he is expected to bag as the primary season moves into its last lap now and his main competitor Senator Cruz is out of the race.
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Cruz, who has engaged in a bitter and nasty war of words with Trump, announced his decision to drop out of the race.
Kasich has made it clear that he is not dropping out of the race.
After Trump's win, the Republican National Committee (RNC) chairman Reince Priebus said that Trump would be the presumptive nominee and asked his party to rally behind him to defeat Clinton in the November polls.
"We are going to make America great again," a confident Trump told supporters at his campaign headquarters in New York as he announced to take on Clinton.
"We are going after Hillary Clinton. She will not be a great president. She will not be a good president. She would be a poor president. She does not understand trade," Trump said, giving a brief glimpse of his campaign against the likely Democratic presidential nominee.
"I want to congratulate Ted Cruz. He is a tough smart competitor," he said of the Texas Senator with whom he had a bitter exchange of words hours before the result of the Indiana primary.
"Ted Cruz is one hell of a competitor. He is an amazing guy. He has got an amazing future. He is one tough competitor," Trump said.