"An aura of inevitability is now forming around the controversial mogul," The Washington Post said after Trump, 69, was endorsed by two House Republican committee chairmen, Bill Shuster and Jeff Miller.
Indiana University basketball coach Bob Knight also threw his support behind Trump's presidential campaign, less than a week before Indiana voters go to the polls in the state's primary.
News reports said more rank-and-file Republicans are expected to follow suit, including longtime Republican lawmaker John Duncan.
"The realisation is that Donald Trump is going to be our nominee. We're coming to the end of the process; it's time to unite the party and take on Hillary," Trump supporter Tom Reed was quoted as saying by The Hill.
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After this Tuesday's primary elections, Trump is now way ahead of his other rivals in terms of delegate count and is about 250 delegates short of the magical figure of 1,237 delegates, which is necessary for him to be the party's presidential nominee.
Trump's early congressional backers, who initially faced scorn for backing the businessman are finding themselves in a more comfortable position, it observed.
"You're not having to stick your neck out quite as far as a few months ago. It's less of a stretch now. People like to be with the winner," Congressman Duncan hunter told the journal.
He was one of the few GOP lawmakers to endorse Trump in March.
A day earlier, Senator Bob Corker Chairman of the Senate Foreign Relations Committee welcomed the foreign policy speech of Trump.
When subsidised foreign steel is dumped into US markets,
threatening factories, the politicians have proven they do nothing, he charged.
"For years, they watched on the sidelines as our jobs vanished and our communities were plunged into Depression-level unemployment. Many of these areas have never recovered and never will unless I become president," he said.
Trump said this wave of globalisation has wiped the middle class totally.
Trump alleged the people who rigged the system are supporting Hillary Clinton because they know as long as she is in charge, nothing is going to change.
"And they want to scare the American people out of voting for the better future. And you have a great future, folks. You gave a great future. These people have given her tens of millions of dollars. My campaign has the absolute opposite message," he said.