The Senate Judiciary Committee will subpoena President Trump’s son Donald Jr. and former campaign manager Paul Manafort if they do not agree to testify next week, the committee’s chairman told RealClearPolitics.

Republican Sen. Chuck Grassley has signed off on the subpoenas along with the ranking Democrat on the committee, Sen. Dianne Feinstein, Grassley confirmed Thursday — meaning no further action would need to be taken should Trump Jr. or Manafort fail to testify.

“We’ve already authorized a subpoena,” said Grassley, adding that the committee would take that next step “almost immediately, if they don’t accept.”

The subpoena would mark a historic moment, with a committee controlled by the sitting president’s own party questioning his eldest child in public.

Manafort and Donald Trump Jr. have not yet responded to the committee’s request, but they will need to do so by Friday, Grassley added. The committee is also hoping to hear testimony from Fusion GPS co-founder Glenn Simpson, who commissioned the unverified but potentially explosive pre-election “dossier” regarding Trump, after Simpson said he was unavailable for a previous hearing.

The Judiciary Committee ratcheted up the pressure on its would-be witnesses Wednesday when it published their names online as scheduled witnesses for the hearing next week — although Manafort, Trump Jr. and Simpson had not yet agreed to appear. Still, the advisory set off a predictable media frenzy as reporters considered the spectacle.

The potential appearance by Manafort and the younger Trump comes after the president’s son disclosed emails earlier this month from June 2016, during the heat of the presidential campaign, in which he expressed interest in receiving damaging information on Hillary Clinton purportedly supplied by the Russian government. Manafort, who was copied on the emails, attended a meeting a few days later with Trump Jr. and his brother-in-law Jared Kushner, who were joined by multiple people with ties to the Kremlin.

These revelations sparked a firestorm, with Democrats and some Republicans calling on Trump Jr. and Manafort speak with the Senate Intelligence Committee, as Kushner now plans to do in closed session Monday. The president’s son tweeted that he would be "happy to work with the committee to pass on what I know."

But, unlike with the Intelligence Committee, testimony before the Judiciary Committee would necessarily unfold in public — training the spotlight squarely on the president’s son at a moment when the administration is already under intense scrutiny.

Reached by phone Thursday, Senate historian Betty Koed could recall just one instance of a sitting president’s child testifying to Congress: when President George H.W. Bush’s son Neil Bush appeared before the House Banking Committee in 1990. But Democrats controlled the House at that time, casting a partisan light on the decision to call Neil Bush as a witness.

President Trump, for his part, has defended his son as a “high-quality guy” and downplayed the meeting with Russian sources, saying recently, “I think from a practical standpoint most people would’ve taken that meeting. It’s called opposition research, or even research into your opponent.”