Politicians of all stripes, including former adversaries, will pay tribute to Republican Senator John McCain at his memorial service in Washington on Saturday.

Former presidents Barack Obama, a Democrat who defeated McCain in the 2008 election, and George W. Bush, who won the 2000 GOP nomination over McCain, are expected to speak at the service at the Washington National Cathedral. Meghan McCain, McCain’s daughter will also speak, along with his close friend former Sen. Joe Lieberman and former Secretary of State Henry Kissinger.

Many other notable figures from both sides of the aisle will also contribute to the ceremony. Of particular note is McCain’s decision to have Russian Vladimir Kara-Murza act as a pallbearer. Kara-Murza, who was twice poisoned while in Russia, is a well-known critic of the Kremlin and Russian President Vladimir Putin.

Saturday's procession began at 9 a.m. ET and paused at the Vietnam Veterans Memorial where McCain's wife Cindy laid a ceremonial wreath. She was escorted to the site by White House Chief of Staff John Kelly and Secretary of Defense James Mattis.

Members of the Armed Forces Body Bearers carried McCain's casket, draped with the American flag, into the cathedral just prior to the service, scheduled to begin at 10 a.m. ET. The senator's family stood to the side as the service members slowly marched up the stairs and through the door.

Before the ceremony, a number of McCain's Senate colleagues, friends, family and numerous notable political and business figures chatted and milled around the National Cathedral.

Notably absent was President Donald Trump, who was asked to stay away from all events during McCain's five-day, cross-country procession. Trump's daughter and senior adviser Ivanka Trump, as well as her husband Jared Kushner, another adviser to the president, were both in attendance.

McCain was highly critical of the president, and his farewell statement written just before he died suggested Trump was fueling "tribal rivalries" and hiding "behind walls."

Trump ignored repeated questions from reporters inside the Oval Office on whether he had any thoughts on the legacy of the late senator.

The White House had lowered its flag to half-staff Saturday night following McCain's death but raised it to full staff Monday morning, sparking outrage from veterans groups and lawmakers.

Later in the day, Trump said in a statement he had signed a proclamation to keep the flag at half-staff through until Sunday's funeral service.

McCain died on Aug. 25 following a battle with brain cancer. He was 81.