Whitaker had served as Sessions' chief of staff.
Whitaker has his supporters too, including a USA senator from Iowa, Joni Ernst.
The White House confirmed that Christie was there Thursday and met with Trump adviser Jared Kushner to discuss prison reform, according to a NJ Advance report. In that role, the telegenic former college football player managed attorneys who prosecuted federal crimes and represented the government in civil matters in half of Iowa.
The deputy attorney-general, now Rosenstein, would normally be in line to become the acting attorney-general, but Trump has complained publicly about Rosenstein, too.
Rewind to last July, before U.S. Senator Lindsey Graham unleashed a sputtering screed in defense of Judge Brett Kavanaugh as senators sought answers for sexual assault allegations against the future Supreme Court justice, when Graham said pretty plainly that if Sessions was somehow removed from the Justice Department, he'd have something to say about it.
Senate Minority Leader Charles Schumer, who has already called on Whitaker to recuse himself from the investigation, said it is "paramount" that Trump's new attorney general protect the Mueller investigation.
In an interview with a conservative talk radio host, Whitaker said there was "no collusion" between Trump's presidential campaign and Russian Federation, a key question being examined by the special counsel's office.
That's raising questions about the fate of Mueller's investigation.
Just before Davis and others addressed the crowd, a motorcyclist pulled close to a group of protesters who were standing on the sidewalk close to Broadway waving signs with anti-Trump and pro-Mueller messages.
Asked whether Whitaker would assume control over Mueller's investigation, Justice Department spokeswoman Sarah Flores said Whitaker would be "in charge of all matters under the purview of the Department of Justice".
Des Moines attorney Guy Cook, a Democrat who has known Whitaker for years, called him a clear thinker and a "no-nonsense guy who is not to be underestimated". "You would have somebody from your campaign take the meeting to try to get the information", he said. They were aimed at protesting the ouster of Sessions, whose recusal allowed Mueller to operate unimpeded, and as a warning that Whitaker should not interfere with the investigation.
"We have to raise our voice and show that we care", said Carolyn Cadigan, who was among more than 100 people who gathered in Joe Marino Park at the corner of East State and Water streets.
Spats between Trump and journalists can sometimes seem circus-like, but critics say the president's hot temper illustrates his deeper disdain for Washington norms - and allegedly for the law. He and his Senate counterpart, California Democrat Sen.
Christie is reportedly a personal friend of Trump's and endorsed him after dropping out of the 2016 presidential campaign himself. She said she wants a firm response from Graham.
Whitaker promised that the organization he led at the time, the Foundation for Accountability and Civic Trust, would "continue to press its investigation into these 17 attorneys general for more information and answers regarding the true motivation and the real agenda behind this reprehensible campaign".
Whitaker grew up in the Des Moines suburb of Ankeny.