Rep. Adam Schiff issed a strongly worded statement to CBS News Tuesday night, condemning Republicans proposing a “witness trade deal” that would have former White House national security advisor, John Bolton, testify in President Donald Trump’s Senate impeachment trial, if former Vice President Joe Biden’s son, Hunter, was also called to the stand.

Schiff blasted the suggestion, calling it an “abuse” of the process, even though his fellow Democrats have been pushing the idea of inviting further witnesses to give testimony in the Senate.

“It would certainly be fair for the president and his team to be able to call witnesses that can provide material information on the charges. It would not be appropriate for the president to seek to call witnesses merely to try to perpetuate the same smear campaign that was foiled when his plot was discovered,” Schiff, who is one of the House Democrats charged with “managing” the prosecution.

“Hunter Biden, for example, can’t tell us anything about whether the president withheld military aid, whether he withheld that aid to coerce Ukraine to conduct political investigations,” Schiff railed. “Or why he wouldn’t meet with the president of Ukraine.”

But Republicans insist that both Hunter and Joe Biden could aid in Trump’s defense, because seeking information on the former Vice President’s involvement in Ukrainian government matters serves a legitimate purpose aside from simply collecting negative information for a future presidential campaign. And beyond that, Republicans say, it’s not clear that Democrats have any use for additional witness testimony other than to plug holes left in the case against Trump by a faulty impeachment inquiry in the House (led, of course, by Schiff).

Senate Minority Leader Chuck Schumer’s (D-NY) proposal for additional witness testimony was soundly defeated Tuesday night, in a marathon Senate session that ran from 1 p.m. all the way until 2 a.m. Wednesday morning. Republicans did not close out the possibility of further testimony, however, and the Senate will take a second vote on the issue after the two sides’ opening statements have concluded. The prosecution and the president’s defense each have two full days available to present their case.

Most GOP Senators are holding their final decision on witnesses until after the presentations have concluded.

In the event that the Senate does ask to hear from witnesses, it will be up to Chief Justice John Roberts, who is the “judge” presiding at the impeachment trial, to determine which witnesses are material to either party’s case.

Schiff denies that Hunter or Joe Biden have anything to offer the President’s case beyond sound bites to use in campaign commercials later on in the presidential election process.

“The only purpose in putting him on their list is they wish to trade material witnesses, like Mr. Bolton and [acting White House chief of staff Mick] Mulvaney and others, for immaterial ones that will allow them to continue to attack a political opponent,” Schiff added in his CBS interview, calling the mere suggestion that Hunter Biden could testify an “abuse” of the Senate process.

“That’s an illegitimate abuse of the trial. And the chief justice, who may have an opportunity to rule on materiality of witnesses, as well as the senators, should not permit that kind of abuse,” he concluded.

Neither Bolton nor Mulvaney has agreed to testify. Bolton noted, earlier in January, that he would submit to a Senate subpoena, if it was issued by Republicans. If the questions veer too close to Bolton’s job as national security advisor, though, his testimony might have to be taken in a closed session, and Bolton may have to plead the Fifth Amendment’s protection against self-incrimination. Mulvaney has been silent on the matter.