President Trump ordered all White House flags to be flown at half-staff Saturday night to honor Sen. John McCain (R-AZ) following news of his death.

This evening, the @WhiteHouse flag has been lowered to half-staff in honor of Senator John McCain… pic.twitter.com/tYdBNK9bA7 — Dan Scavino Jr. (@Scavino45) August 26, 2018

McCain passed away at the age of 81 after months of fighting an aggressive form of brain cancer.

The president, who had sparred with McCain throughout the 2016 presidential campaign, also paid tribute to the late Arizona senator, tweeting his condolences Saturday evening once McCain’s office released a statement announcing the senator’s death:

My deepest sympathies and respect go out to the family of Senator John McCain. Our hearts and prayers are with you! — Donald J. Trump (@realDonaldTrump) August 26, 2018

It is up to a president to decide who should be honored with flags at half-staff, and those orders are usually made by presidential proclamation. But traditionally, sitting senators who die while in office have flags lowered in their honor from their time of death until their burial.

Arizona Gov. Doug Ducey also ordered that flags be flown at half-staff when news of McCain’s death broke:

I have ordered all flags be lowered to half-staff in honor and remembrance of the incredible life of @SenJohnMcCain. May God rest his soul and look over his entire family. Our state and our nation mourn together. #JohnMcCain #CountryFirst https://t.co/Bj9pgsLIon — Doug Ducey (@dougducey) August 26, 2018

“May God rest his soul and look over his entire family. Our state and our nation mourn together,” Ducey’s statement read in part.

McCain led a 31-year career in the Senate after spending years in the Navy, where he once endured capture as a prisoner of war in Vietnam.