GOP senator: Trump has changed presidency 'not necessarily toward the positive'

"I think so, not necessarily toward the positive either," Johnson said during an interview in Wisconsin with WTMJ. 
Johnson added that former President Clinton had also shifted the "behavior and the standard of the presidency."
"It's unfortunate. I revere our Constitution. I revere these institutions, including the office of the presidency. It would be nice if everybody conducted themselves, I guess, the way we would here in Wisconsin," Johnson continued. 
Johnson was asked about Trump's behavior, but didn't point to a specific incident during the interview. His comments come as Congress is locked in an impeachment fight fueled by the president's interactions with the leader of Ukraine.
Johnson, who has emerged as one of Trump's most vocal supporters on Ukraine, said on Monday that "there has been a concerted effort from Day 1 to sabotage this administration." 
"I don't agree with everything he's doing, but I have to give him a great deal of credit," Johnson said. 
The White House last week released a partial transcript of Trump's call with Ukrainian President Volodymyr Zelensky. In the call, according to the document, Trump asked Zelensky to work with his personal attorney Rudy GiulianiRudy GiulianiGraham invites Giuliani to testify about recent Ukraine trip Judge orders State Dept. to search for and provide more Ukraine docs DOJ releases memos backing Trump immunity claims ahead of impeachment vote MORE, and expressed hope that he “can look into” former Vice President Joe BidenJoe BidenNew York Times editorial board calls for Trump's impeachment Graham invites Giuliani to testify about recent Ukraine trip Booker leads other 2020 Dems in petition urging DNC to change debate qualifications MORE and his son.
Johnson said on Monday that there was no "quid pro quo" in the Trump call, but that he has "a lot of questions" about Ukraine and Democrats. 
"Everybody says well there's no evidence, all these things have been debunked. ... [But] I have all kinds of questions dating back to Hillary ClintonHillary Diane Rodham ClintonNo, the polls aren't wrong — but you have to know what to look for How to shut down fake Republican outrage over 'spying' on Trump More than 200,000 Wisconsin voters will be removed from the rolls MORE's email scandal," Johnson said. 
Johnson has also called for an investigation into Biden, including suggesting that a Senate investigation would be "completely appropriate."