Things have taken a turn for the dramatic in the ongoing bribery trial involving Democratic Senator Bob Menendez. Prosecutors say he accepted bribes from a deep-pocketed benefactor and in return lobbied government officials to benefit his “hermano.” If he is found guilty and steps down from office, Republican Gov. Chris Christie could choose his successor—which would likely change the political makeup of the U.S. Senate.

Justice Department officials say that Menendez met with top officials at the Center for Medicare and Medicaid Services to help a wealthy eye doctor—Salamon Melgen, who is on trial alongside the senator—get out of an $8.9 million billing dispute. Melgen was convicted of Medicare fraud over the case earlier this year. In exchange, Menendez was rewarded with lavish vacations, private plane rides, and more than $750,000 in campaign contributions.

On Monday, Jonathan Blum, a former principal deputy administrator at CMS, testified that Menendez tried to pressure the bureaucrat into changing the agency’s billing rules so as to “relieve or forgive or lessen” the Florida doctor’s over-payment, CNN reports.

During a 2009 phone call, Blum told Menendez the agency would not amend the policy, spurring the Democratic senator to get “hostile” and hang up the phone. While Menendez never mentioned the doctor by name, Blum knew that the specific policy only involved the Florida ophthalmologist.

“I was very curious why the senator was focused on this case and asked the staff several times,” Blum said, according to Politico. “The senator is from New Jersey. The physician is based in Florida. I pressed our staff several times on the connection between the senator and Dr. Melgen.”

Blum also testified that then-Senate Majority Leader Harry Reid, a Democrat, arranged a meeting about the billing dispute in 2012 with Menendez and former Health and Human Services Secretary Kathleen Sebelius. When Blum reiterated that the agency’s policy would not be amended to help the wealthy eye doctor, Menedez got angry.

“I found the tone to be very angry, very hostile,” Blum said. “I found that I was being put on the defensive and it was a very angry exchange.”

On Tuesday, prosecutors called on former CMS head Marilyn Tavenner to testify, and Sebelius is set to testify this week. Reid is also expected to testify about the meetings and the pressure prosecutors say he faced from his colleague to help Melgen.

An overwhelming majority of New Jersey voters (84 percent) think their senator should resign if he’s convicted, but Democrats are keeping quiet about the trial, or even defending Menendez. On Sunday, Sen. Bernie Sanders told CNN’s Jake Tapper he wouldn’t comment on the trial.

“Whoa, whoa, whoa, I think, in this country, people are entitled to due process,” Sanders said. “Let the process take its course.”

Sen. Chuck Schumer said his colleague was issuing a “spirited defense” and Sen. Kamala Harris, who is rumored to be eyeing a 2020 presidential bid, has been giving everyone the silent treatment.