He said it would be "inappropriate", but not impeachable, for a president to ask a foreign leader to investigate a political rival, as Trump is alleged to have done.
The scattered and sometimes contradictory White House response to the allegations made by a parade of impeachment witnesses who have testified behind closed doors over the past several weeks were reflected in appearances by several senior Republican lawmakers on Sunday's news-talk shows. (Sipa USA) A whistleblower raised concerns about Mr Trump's July 25 call with Ukrainian President Volodymyr Zelenskiy, in which he pressed Mr Zelenskiy to investigate Mr Trump's political rivals.
Later, Graham said identifying the whistleblower will be necessary if the impeachment case against the president moves forward.
However, "I do not believe it was impeachable", the Texas Republican said, making the freakish argument that the public has gotten used to Trump publicly making the kind of comments heard in his call with Ukraine.
At campaign-style rallies, including one in Louisiana last week, Trump has again and again called for publication of the whistleblower's identity, drawing sharp objections from the individual's legal team.
A review of more than 2600 pages of transcripts released this week from eight witnesses who have testified in the House impeachment inquiry over the past six weeks shows how controversy over Mr Trump's Ukraine policy had been brewing inside the USA government for months.
On NBC's "Meet the Press", Sen.
"There's a reason we let murderers and robbers and rapists go free when their due process rights have been violated", he said, saying you can not "sweep process under the rug".
While breaking ranks with fellow Republicans over the call for the whistleblower's testimony, Hurd said in his "Fox News Sunday" interview that he agreed the younger Biden should be called to appear.
"It's impossible to bring this case forward, in my view, fairly without us knowing who the whistleblower is and having a chance to cross-examine them about any biases they may have", he said.
Former U.S. Ambassador to Ukraine Marie Yovanovitch is expected to testify Friday. Will Hurd, R-Texas, said the impeachment inquiry "has been a partisan exercise from the very beginning". "I don't hear that". He said Republicans want to hear testimony from Hunter Biden.
Another Democrat on the Intelligence Committee, Rep. Sean Patrick Maloney of NY, also rejected the call for Hunter Biden to testify. "So the thing is I think it's a mistake to say, 'Oh, he withheld aid, until he got what he wanted.' Well, if it's corruption, and he believes there to be corruption, he has every right to withhold aid".
Another GOP senator, Ron Johnson of Wisconsin, said on CNN's "State of the Union" that officials' closed-door testimony offered so far did not establish that Trump's motive in pressuring Zelensky was personal political gain.