House Intelligence Chairman Adam SchiffAdam Bennett SchiffSchiff says committees are making 'rapid progress' in impeachment probe Trump rages against 'garbage' Ukraine probe ahead of latest witness deposition Mark Zuckerberg deserves praise for his noble stand on free speech MORE (D-Calif.) said President TrumpDonald John Trump Comey: Mueller 'didn't succeed in his mission because there was inadequate transparency' During deposition, official says he made several efforts to advocate for Marie Yovanovitch Bolton looms large as impeachment inquiry accelerates MORE’s former national security adviser John BoltonJohn BoltonBolton looms large as impeachment inquiry accelerates US restores trade benefit to Ukraine after delay Key witness in impeachment investigation asks federal judge to rule on testifying MORE is a “very important” witness in the ongoing impeachment probe. 

Schiff added on ABC's "This Week" that Bolton has emerged from testimony others have given during closed-door depositions as a key witness.

“Obviously he has very relevant information and we do want him to come in and testify,” Schiff added.

"John Bolton is a very important witness...and we do want him to come in and testify," Rep. Adam Schiff tells @ThisWeekABC, adding that he predicts the White House may to try to block any possible testimony by Bolton. https://t.co/BURjYQzzys pic.twitter.com/5eV3nwlyfk

— This Week (@ThisWeekABC) October 27, 2019 

But the chair of the House Intelligence Committee indicated the White House may try to block Bolton from testifying. 

He said the White House has tried to obstruct the investigation and witnesses coming in. 

“My guess is they're going to fight us having john bolton in,” Schiff said.

The White House’s “obstruction” is one reason Schiff said he is hesitant to give a timeline of when the House will hold public hearings. 

“We will be doing public hearings and I think we'll be doing them soon,” Schiff said. 

“I don't want to give precise timing because, in part, we’re struggling with the White Houses's continuing efforts to obstruct our investigation,” he added.

The witness depositions have so far been limited to members of three House committees involved in the inquiry.