The U.S. Senate is voting now to override President Obama's veto of a bill that would allow families of 9/11 victims to sue Saudi Arabia. If two-thirds of the House and Senate vote to override the president's veto, it would mark the first successful veto override in Obama's tenure. The House is expected to take up the vote between 2:45 p.m. ET and 3:15 p.m. ET, according to NBC News reporter Alex Moe.