President Donald Trump’s veto of a joint resolution to put an end to U.S. support for the Saudi-led war in Yemen is going to kick the matter back to senators when they return to the Capitol next week.

With recess continuing this week, senators are in their home states, on congressional delegations abroad and on the presidential campaign trail. But Vermont independent Sen. Bernie Sanders , one of the many Democratic presidential candidates, took a moment Monday to circulate a dear colleague letter seeking support for overriding the Trump veto.

“For far too long Congress, under both Democratic and Republican administrations, has abdicated its Constitutional role with regard to the authorization of war,” Sanders wrote to his Senate colleagues. “The historic passage of this resolution, the first time since the 1973 War Powers Resolution was passed that it has been successfully used to withdraw the United States from an unauthorized war, was a long overdue step by Congress to reassert that authority.”

“The Congress must now act to protect that constitutional responsibility by overriding the president’s veto,” Sanders wrote.

Sanders, who has been out on the presidential campaign trail himself, wrote in the letter that supporters of the American involvement in Saudi Arabia’s Yemen campaign should seek a floor debate and and vote on that effort.