• Sen. John Fetterman urged Sen. Bob Menendez to step down in the face of federal bribery charges.
• Fetterman is the first Democratic senator to call for Menendez's resignation, though he follows a flurry of similar calls from state leaders.
• New Jersey Gov. Phil Murphy, the state's General Assembly speaker and the Democratic State Committee chairman all called for the indicted senator to resign on Friday.
• "I hope he chooses an honorable exit and focuses on his trial," Fetterman said about Menendez, New Jersey's senior senator.

John Fetterman of Pennsylvania on Saturday became the first Democratic U.S. senator to call on Sen. Bob Menendez of New Jersey to resign in the face of a criminal bribery indictment unsealed Friday.

"He's entitled to the presumption of innocence, but he cannot continue to wield influence over national policy, especially given the serious and specific nature of the allegations," Fetterman said on Saturday. "I hope he chooses an honorable exit and focuses on his trial."

Fetterman's statement joins a chorus of cries for the newly indicted Democratic senator to step down.

Menendez is expected to hold a press conference on Monday in Hudson County, New Jersey, where he got his start in politics, a source directly involved with the planning told NBC News.

Menendez is also expected to say he does not intend to resign, according to this source.

On Friday, New Jersey Gov. Phil Murphy, the state's General Assembly speaker and the Democratic State Committee chairman all called on Menendez to resign after their fellow Democrat was indicted.

"The allegations in the indictment against Senator Menendez and four other defendants are deeply disturbing," Murphy said about Menendez, the state's senior senator.

"These are serious charges that implicate national security and the integrity of our criminal justice system," said Murphy.

"The alleged facts are so serious that they compromise the ability of Senator Menendez to effectively represent the people of our state. Therefore, I am calling for his immediate resignation."

Assembly Speaker Craig Coughlin said, "The charges laid out against Senator Menendez today go against everything we should believe as public servants.

"We are given the public's trust, and once that trust is broken, we cannot continue," Coughlin said, adding that Menendez must resign to "allow New Jersey, and America, to move forward."

Democratic State Committee chairman LeRoy Jones, Jr. said Menendez should step down "in the interest of ensuring that New Jerseyans continue to be granted the federal representation that they deserve."

Jones also noted the upcoming state legislative elections in November, and said Menendez's resignation would allow the Democratic party "to keep its focus" on state-level races.

New Jersey Democrats in Congress including U.S. Reps. Andy Kim and Mikie Sherrill also called on Menendez to resign.

Menendez responded to his critics late Friday. "Those who believe in justice believe in innocence until proven guilty. I intend to continue to fight for the people of New Jersey with the same success I've had for the past five decades," he said in a statement.

"This is the same record of success these very same leaders have lauded all along. It is not lost on me how quickly some are rushing to judge a Latino and push him out of his seat. I am not going anywhere," he added. 

The statement hinted at how bitter the debate over the senator's political future is likely to become.

Despite Menendez's defiance, calls for his resignation continued over the weekend.

Along with Fetterman, Reps. Josh Gottheimer and Donald Norcross on Saturday also urged Menendez to step down. Norcross is a longtime South Jersey congressman who has openly supported Menendez in the past. His brother, George Norcross, was formerly a Democratic power broker in South Jersey with massive influence who also helped fundraise for Menendez's campaigns.

"Although the Senator has many accomplishments over his decades in public service, we cannot be distracted. For that reason, Senator Menendez should step aside in order to deal with these allegations," Rep. Donald Norcross said in a statement.

Menendez, 69, and his wife, Nadine Menendez, were indicted on three criminal counts, along with three New Jersey businessmen who were charged with two of the counts.

The couple is accused of having taken hundreds of thousands of dollars in bribes over at least four years, while the senator performed, in return, political favors for the three businessmen.

Prosecutors allege the favors included providing sensitive national security information to Egyptian officials.

Menendez insisted he and his wife had nothing wrong, and accused prosecutors in a statement of having "misrepresented the normal work of a Congressional office."

He did not address the specific charges other than to say the "facts are not as presented."

U.S. Senate Majority Leader Chuck Schumer, a New York Democrat, in a statement said, "Bob Menendez has been a dedicated public servant and is always fighting hard for the people of New Jersey."

Menendez was appointed to the Senate in 2005, but went on to win reelection on his own three times, and will face voters again in 2024. Democrats have a difficult Senate map next year, when they will be defending 23 of the 33 contested Senate seats.

In states that are dominated by just one political party, as New Jersey is by Democrats, Senate seats change hands far less than they do in swing states, where elections tend to be more competitive.

In New Jersey, for example, only four people have been elected to the U.S. Senate in the past 23 years, the last one being Sen. Cory Booker in 2013.

In the event that Menendez was to resign or retire when his current term ends, the race to fill his Senate seat would likely draw a who's who of the state's elected Democrats. Some of the top names already being floated Friday were Gottheimer, Kim, Norcross and Sherrill.

Kim on Saturday officially announced his senate campaign, noting that Menendez's refusal to resign "compelled" him to enter the race.

New Jersey Attorney General Matthew Platkin in a statement late Friday afternoon said, "The allegations are deeply disturbing to me and my Office, and we are already in the process of reviewing the concerns raised by the indictment."

"As the now unsealed indictment makes clear, there are allegations that Menendez attempted to pressure a senior member of this Office under a prior administration," Platkin said.

"The conduct alleged in the indictment occurred prior to my tenure as Attorney General, and involved a matter that was resolved prior to my time in office. My Office has cooperated fully with the Southern District of New York's investigation. We will continue to do so. We are also engaged in our own independent internal inquiry into the allegations set forth in the indictment."