"I do not consider it a criminal offense, and I think the house, frankly, has made the case under certain assumptions," he said.
In Ukraine, there is no evidence of misconduct by Joe or Hunter Biden. There is also no evidence that the former vice president has received money from China, and a lawyer from Hunter Biden has pushed back Trump's characterization and described it as "gross misrepresentation". Speaker of the House, Nancy Pelosi, said Trump betrayed his oath of office last month and announced that he would initiate a formal impeachment trial against the president.
Growing controversy stems from a whistleblower complaint alleging that Trump used his official powers in the 2020 elections to solicit "interference" from Ukraine and that the White House had taken steps to to cover up this. Trump has denied any wrongdoing.
A rough copy published by the White House shows that Trump has repeatedly urged Ukrainian President Volodymyr Zelensky in a July phone call to investigate Joe and Hunter Biden.
Portman also said Monday that the impeachment investigation and the considerable attention it attracts mean that it will be even more difficult to convict Congress of bipartisan laws.
"It's sad for me how hard it is to do things in Washington, now it gets even more difficult, and as divided as our country is already, we'll be even more polarized," he said.
"I know there are strong feelings on both sides, but we have to be very careful, I think."