"I am not going to discuss the specifics of interactions that I may or may have not had with the President", Rogers said, adding he has never felt pressured to do anything unethical.
At the Wednesday hearing, National Security Agency Director Mike Rogers also is expected to face questions about whether he faced pressure from Trump to rebut the stories about potential collusion between Trump associates and Russian officials. "I have never felt pressured to interfere or intervene in shaping intelligence in any way", he said.
Coats says he is not sure he has a legal basis for refusing.
Comey will testify before the committee Thursday on conversations he had with Trump before his firing.
Early Wednesday, Trump announced his pick to succeed Comey at the FBI - Chrstopher Wray, a former Justice Department official who served as New Jersey Gov. Chris Christie's lawyer during the George Washington Bridge lane-closing investigation.
The hearing brought four senior intelligence and law enforcement officials before the committee on Wednesday.
This appeared to frustrate some members of the committee, who asked why Mueller's questions would be answered when they, as Senate-confirmed officials, had an obligation to tell Congress the truth.
Comey also said Mr Trump demanded he pledge his loyalty in a White House meeting on January 27, just days after he took office under the cloud of allegations that Russia's interference helped him win election.
McCabe repeated he would not comment on the conversation he'd had with Comey or about ones Comey may have had with Trump, to Heinrich's seeming consternation.
Both declined to discuss their conversations with Trump, answering in general terms.
"Director Coats said he'd be happy to tell the whole truth before the appropriate committee", Virginia Sen.
The former Federal Bureau of Investigation director, James Comey, who was sacked by Trump on May 9, is scheduled to testify before the same committee Thursday morning. John McCain and Intelligence Chairman Richard Burr both spoke up to tell her to give the witnesses a chance to answer her questions. Mark Warner, respectively, said in their opening statements that it was in the US' national security interests to authorize Section 702 intelligence collection.
Trump has sometimes pointed to that memo to justify sacking Comey, and on other occasions has said he would have fired him anyway, referring to the Russian investigation as a factor.
While Democrats have focused on possible collusion between Russian Federation and the Trump campaign, Republicans have focused on leaks about the investigation.
Wednesday's hearing was supposed to focus on the Foreign Intelligence Surveillance Act, the law that governs how USA intelligence agencies conduct electronic surveillance and collect information between foreign powers and "agents of foreign powers" suspected of terrorism.