"Shifts in the poll numbers supporting Trump have demonstrated this. The establishment has begun the process of warming to him and feeling him out on specific policies," Mahaffee said.

With the nomination out of the way, Trump can now focus his attention and strategy on Clinton. The bombastic businessman has begun forming a narrative about his political rival, calling her "crooked Hillary," in an effort to paint her as dishonest and untrustworthy.

"If crooked Hillary Clinton is in charge, things will get much worse," Trump said on Thursday at a rally, saying that Clinton would bury businesses in regulations that would be difficult to navigate.

That would further slow the economy that has still not fully recovered from the 2008 economic nosedive, Trump implied.

Indeed, Clinton is currently embroiled in a scandal over whether she jeopardized US national security by using a private email account and server for official business while she was Secretary of State under President Barack Obama.

A House panel is also investigating Clinton's responsibility for the 2012 terror attack on the US consulate in Benghazi, Libya, in which four Americans including US Ambassador Chris Stevens were killed, when Clinton was then secretary of state.

After clinching the nomination, Trump is highly likely to go on full attack mode against Clinton and use this and other Clinton scandals as political fodder against the former first lady.

"Being the nominee allows Trump to pivot to the fall campaign and focus all his energy on defeating Hillary Clinton," West said.

This victory frees up resources for Trump and will allow him to moderate some of his policy messages, he said.

Trump "now is in full control of the party platform and the summer convention so he will mold each of those to his own preferences," West added.