Democratic Sen. Robert Menendez will resign next month after corruption conviction

Democratic Sen. Robert Menendez will resign next month after he was found guilty on all 16 counts in a federal bribery and corruption trial, three sources familiar with the matter told NBC News.

Menendez will leave office on Aug. 20, the sources said, with two saying he has informed some of his staff. One of the sources close to Menendez said the senator has written his letter of resignation, is submitting it and will resign.

His date of departure was first reported by the New Jersey Globe.

As NBC News first reported last week, Menendez had begun calling allies telling them he would step down from the Senate after he was convicted by a jury of accepting bribes, including gold bars and cash, for official actions to benefit Qatar and Egypt. He is set to be sentenced on Oct. 29, though he has vowed to appeal.

Nearly every Democratic senator, as well as House members and other key elected officials in New Jersey, had said Menendez needed to resign his seat, making it untenable for him to continue. Some had threatened to force a vote to expel him from the Senate if he did not leave voluntarily.

Menendez is also under investigation by the Senate Ethics Committee which said in a statement Monday that it had initiated an "adjudicatory review," which is a required step before making a recommendation to the full Senate to expel or otherwise discipline a senator. The committee said it had notified Menendez and his attorneys that the committee unanimously voted to open the review.

Rep. Andy Kim, D-N.J., is running for Menendez's seat in November against Republican Curtis Bashaw. Menendez had filed to run for re-election as an independent, saying he would continue the campaign if exonerated.

Menendez served as mayor of Union City,