WASHINGTON (AP) — Kamala Harris and Cory Booker have each missed more than one-fifth of the Senate’s votes so far this year as they campaign for president, according to an Associated Press analysis of congressional data.

With 16 missed votes of the 77 that the Republican-controlled Senate have held in 2019, Harris and Booker far outpace the number missed by their fellow senators also vying for the Democratic presidential nomination. Sen. Bernie Sanders has missed seven votes so far this year, while Sens. Kirsten Gillibrand and Amy Klobuchar have each missed three and Sen. Elizabeth Warren has missed one vote, the AP found.

Seeking the presidency as a sitting member of Congress requires a logistical juggling act that often results in candidates taking hits for missed votes as the pace of campaign season picks up. Perhaps the most notable recent example is Florida Sen. Marco Rubio, who took hits for his missed votes from his rivals — including future President Donald Trump — during the 2016 GOP presidential primary.

“When you’re a governor or businessman, you can run for president and still do your day job. But when you’re a senator or congressman and run for president, you’re not voting, which is the single most important part of your job,” said Alex Conant, a veteran Republican strategist and Rubio’s communications director in 2016. “So I think there’s an inherent conflict that people (who) aren’t in that position are going to try to exploit.”

That doesn’t mean, however, that jabbing at presidential candidates for missed votes is effective. While Rubio’s absenteeism drew criticism from Trump as well as from the Democrat seeking to take his Senate seat in 2016, he still easily won reelection.

And Rubio had missed considerably more votes at a similar point in 2015 than Harris and Booker have during 2019’s Senate session so far: The Republican was absent from 25 of the first 77 votes of that year, according to the AP’s tally. That is 56% more votes than Harris and Booker missed.

Texas Sen. Ted Cruz also took heat for missed votes from his opponent last year, former congressman turned Democratic presidential hopeful Beto O’Rourke, and still came out ahead.