Alan Dershowitz, who joined Donald Trump's legal team during the former president's first impeachment trial in 2020, told right-wing news network Newsmax that he has "no idea" why the former president's current counsel opened his remarks by praising US Senators during Mr Trump's second trial.
Bruce Castor said Democratic impeachment managers gave an "outstanding presentation" and called Senators acting as jurors in the trial "extraordinary people, in the technical sense."
"You will not hear any member of the team representing former President Trump say anything but in the strongest possible way denounce the violence of the rioters and those that breached the Capitol," he said.
"There is no argument. I have no idea what he is doing," Mr Dershowitz told the network moments after Mr Castor's opening remarks. "That's not the kind of argument I would have made, I’ll tell you that."
Read more: Follow live updates from Trump's second impeachment trial
The former Trump attorney has previously said he believes that the former president's remarks during a rally as his supporters broke into the Capitol building on 6 January was constitutionally protected speech.
In their opening statements, Democratic House impeachment managers led by Congressman Jamie Raskin screened a 10-minute compilation of the assault, airing inside the chamber that was under attack just one month earlier.
Congressman Raskin also delivered emotional remarks, invoking the personal tragedies surrounding the attack, just days after the death of his 25-year old son Tommy. The congressman was joined by his daughter and son-in-law at the Capitol on 6 January, and he pleaded with a colleague to protect them.
"C'mon," Mr Dershowitz told Newsmax, cutting away from Mr Castor's opening statement. "The American people are entitled to an argument. ... This, just after all kinds of very strong presentations from the House managers with the video tapes and the emotional speech by Congressman Raskin, my former student – you know, you get up there and respond.
"Maybe he'll bring it home, but right now, it does not appear to me to be effective advocacy," he said.
Mr Trump was impeached last month in the House of Representatives on a count of incitement of insurrection following his comments and a months-long campaign to undermine the results of the 2020 presidential election with false election fraud claims, baseless conspiracy theories and spurious legal challenges.
An impeachment trial in the Senate opened on Tuesday and is expected to carry into next week.
