Every member's availability for key votes could end up being consequential as the bitterly divided chamber is set to tackle a slew of high-profile issues from voting on emergency funding for Hurricane Harvey, raising the debt ceiling, passing a budget and enacting tax reform.
Here's a look at how two very different personal stories could resonate in Congress this session.
Arizona Republican Sen. John McCain
is being treated for an aggressive form of brain cancer. But after completing chemotherapy treatments over the summer break his office stressed he's returning, to continue "his work for the people of Arizona and the nation."
First up for the 81-year-old Republican is managing the annual defense bill, a massive piece of legislation that sets Pentagon policies and spending priorities. Throughout McCain's high-profile and globetrotting political career, it is his quieter work on the Armed Services Committee -- where he is now the chairman -- in which he seems to take the most pride. So, it is fitting that he will be on the floor again to see the bill through.
When McCain was last in the Capitol, just after his cancer diagnosis, he delivered a stern rebuke to his colleagues for the partisanship that has gripped the Senate. He then stunned the nation with a dramatic middle-of the-night vote
against repealing the Affordable Care Act, crippling the Republicans' top legislative priority.
President Donald Trump has not hidden his anger with that vote, and McCain has never been shy of breaking with the President or his own leadership.
In a Washington Post op-ed Friday
, McCain continued to prod his colleagues to do a better job.
"Congress will return from recess next week facing continued gridlock as we lurch from one self-created crisis to another," he said. "We are proving inadequate not only to our most difficult problems but also to routine duties."
New Jersey Democratic Sen. Robert Menendez
New Jersey Democratic Sen. Robert Menendez will be sidelined next month in facing what could be career-ending criminal trial.
The third-term New Jersey senator, who recently served as the top Democrat on the Senate Foreign Relations Committee, goes on trial in Newark on Wednesday on charges of 18 counts of fraud and bribery. Menendez is accused of taking gifts, including luxurious vacations and large campaign contributions, from a Florida ophthalmologist -- a co-defendant in the case -- who the senator is accused of helping with matters before the government, including disputes over Medicare reimbursements.
Menendez has said he did nothing wrong, maintaining that he and the doctor are old friends and therefore the gifts are legal.
He is first sitting senator to be indicted in nine years. The last was Alaska's Republican Ted Stevens, whose conviction was eventually dropped because of prosecutorial misconduct
Menendez tried to get a special dispensation from the court to halt the trial occasionally so he could return to DC for critical Senate votes. But US District Court Judge William H. Walls rejected the request
. The judge said Menendez is no different than a "cab driver" or "radio repairman" and suspected he was trying to "impress the jurors with the public importance of the defendant senator and his duties."
Menendez is not required to be in court, but if he were to skip parts of the trial, it could send a negative signal to the jury.
If found guilty, Menendez's situation presents Senate Democrats with the awkward question of whether he should be forced to resign, a situation that poses a political problem for their caucus.
Any vacancy would be filled by the Republican Gov. Chris Christie and give Senate Republicans another vote in already bitterly divided chamber.