Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) is undergoing hernia surgery on Monday.

The 74-year-old senator, who is running for the Democratic presidential nomination, is having an "elective outpatient hernia repair procedure," according to his Senate office. The surgery is taking place at George Washington University Hospital in Washington, D.C.

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His office added that Sanders is expected to "resume his Senate duties" and be back to work on Tuesday.

The Senate is expected to vote Monday evening on Gayle Smith's nomination to lead the United States Agency for International Development (USAID). The procedure means that Sanders will miss that vote.

Sanders has missed 15, out of more than 300, roll call votes so far this year, according to GovTrack.

Democrats have criticized Republicans for a month over the pace of nomination votes, suggesting that by blocking Smith and other foreign policy and national security nominations, Republicans were undercutting the administration's ability to combat the Syrian humanitarian crisis.

Majority Leader Mitch McConnell (R-Ky.) scheduled Monday's vote on Smith's nomination before lawmakers left Washington for a week-long Thanksgiving recess.

However, Sen. Jeanne Shaheen (D-N.H.) suggested at the time that "there are many other nominees that are ready to serve their country in our foreign policy and national security agencies but are stuck waiting in the wings."

This story was updated at 3:03 p.m.