Sens. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.) and Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.), who are among the six Democratic senators running for the White House, have missed the most votes in the Senate so far this year.

Booker and Harris have both missed 16 roll call votes on the Senate floor, according to a Hill analysis of the 77 total roll call votes the Senate has held since the start of the 116th Congress in January.

Spokespeople for Booker's and Harris's Senate offices didn't immediately respond to a request for comment about their votes. Their absences didn't change the ultimate outcome of any of the votes.

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Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.) has missed seven votes so far this year, according to The Hill's analysis, including a vote where Republicans squashed an effort to block the Trump administration from lifting sanctions against three business connected to Russian oligarch Oleg Deripaska.

Sens. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.) and Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.), who are also running for the party's nomination, have missed three votes each, while Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) has missed one vote.

Harris's missed votes include David Bernhardt's nomination to be Interior and a slate of district judges.

She was campaigning in Iowa last Thursday, the same day the Senate held its final vote on Bernhardt.

Harris did put a statement into the Congressional Record specifying that had she been present, she would have opposed his nomination.

"I was absent for vote No. 77 on Executive Calendar No. 200, the nomination of David Bernhardt to be Secretary of the Interior. Had I been present, I would have voted no on the nomination," Harris wrote.

Harris also missed the two votes where Republicans used the "nuclear option" to speed up confirmation of most of Trump's nominees, as well as two failed votes on a stalled disaster aid package meant to respond to a spate of recent storms, wildfires and hurricanes.

Republicans criticized her for missing the disaster recovery votes, with the conservative group America Rising arguing that "running for president is more important to Harris than helping Californians."

Booker's missed votes also include Bernhardt's nomination and a slate of district judges, both of which would have been able to pass without any Democratic support, assuming the Senate's Republicans were present.

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Booker, a member of the Foreign Relations Committee, was also the only senator to miss the vote confirming John Abizaid as U.S. ambassador to Saudi Arabia. He also missed the formal roll out of Sanders's "Medicare for All" bill, which he is supporting, but spoke at the North America’s Building Trades Unions conference in Washington on the same day.

Republicans have also missed some roll call votes this year.

Sen. David Perdue (R-Ga.), who is up for reelection to his Senate seat next year, has missed 11 roll call votes so far this year, putting him in third place behind Harris and Booker for the number of missed Senate floor votes.

After that are Sens. Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R-N.C.) and Kyrsten Sinema (D-Ariz.) who have both missed eight votes, and Sen. Rand Paul Randal (Rand) Howard PaulRand Paul says he can't judge 'guilt or innocence' in Breonna Taylor case Overnight Health Care: Health officials tell public to trust in science | Despair at CDC under Trump influence | A new vaccine phase 3 trial starts Health officials tell public to trust in science MORE (R-Ky.), who has missed seven. None of the three senators are up for reelection in 2020.

It also isn’t the first time senators vying for their party's presidential nomination have missed Senate votes.

Sen. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (R-Texas), who was in the middle of a White House bid, and Sanders led the Senate for the most votes missed during the first quarter of 2016. Cruz and Sens. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE (R-Fla.) and Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.), who both ran for president in 2016, also missed the most Senate votes in 2015.

Rubio, who had the worst attendance record, missed 35 percent, or 120 of the 339 roll votes, during the past year, according to GovTrack at the time.