Sen. John Cornyn (R-Texas) and Rep. Brad Sherman (D-Calif.) are urging their respective party leaders to require presidential and vice presidential nominees to name “successors” as part of a new comprehensive proposal to establish a clear line of presidential succession.

The two Members made the request in writing to Republican National Committee Chairman Ken Mehlman and Democratic National Committee Chairman Howard Dean on Wednesday after unveiling bipartisan legislation that would modify the law governing the presidential line of succession.

“One of the primary areas of concern is the period between the nominating conventions and the casting of Electoral votes,” Cornyn and Sherman wrote the two party leaders. “Should a presidential or vice-presidential nominee be unable to proceed as a nominee between these two events, general election voters and electors would face great uncertainty about their votes.

“We are concerned about the potential mischief and instability in our government that could arise in such event,” the two Members added. Should the presidential nominee become the only person incapacitated, the vice presidential candidate would replace him, the Members said.

RNC and DNC spokespeople declined to comment on the proposal.

The Presidential Succession Act of 2005 also seeks to codify an acting president’s power until a new president is elected and recommends that the outgoing president work closely with the incoming administration on the appointment of Cabinet secretaries, all of whom will fall in the presidential line of succession.

The legislation calls for the lame-duck president to nominate the president-elect’s Cabinet choices and asks the Senate to approve them “to the extent it deems appropriate prior to the inaugural event.”

The outgoing president would then appoint these Cabinet members before the new president was sworn into office.

While the legislation maintains the status of the House Speaker and the Senate President Pro Tem in the presidential line of succession, it does curb the positions’ powers in one respect. If the president, vice president, Speaker and President Pro Tem all die around the same time, the acting presidency would be awarded to the highest-ranking eligible Cabinet member, rather than to a Speaker or President Pro Tem hastily elected by Congress during the power vacuum.

“I cannot think of a worse time to have two presidents with equal claims to the office, perhaps from different parties, than at a time of national crisis … perhaps due to terrorism or assassination,” Sherman said.

The two Members said it is critical for Congress to address the confusing presidential succession situation, given the rise of terrorist acts directed at the United States such as the Sept. 11, 2001, attacks.

“We now live in a period of time where no one can say, ‘Oh, we hadn’t thought of the idea that terrorists would try to kill our national leaders and leave us leaderless,’” Sherman said. “We have been warned.”

Even though personal relations between the two political parties on Capitol Hill are damaged, Cornyn pleaded with his colleagues on both sides of the aisle not to allow this legislation to fall through the cracks.

“This really should not get hung up on partisan politics,” he said. “This really should not be controversial.”

In addition to the other changes, the legislation would place the Homeland Security secretary — a position created in the 108th Congress in response to the new terrorism threat — at the end of the current succession line, followed by five high-profile U.S. ambassadors.

The U.S. ambassador to the United Nations and the U.S. ambassadors to the four permanent countries on the United Nations Security Council — Great Britain, Russia, China and France — would all join the line of succession. Since the ambassadors work outside of Washington, D.C., it would make continuity much more likely in the event of a “catastrophic” attack in the nation’s capital, Cornyn and Sherman said.

The decision to add ambassadors to the presidential line of succession comes at a time when Democrats and Republicans are divided over John Bolton’s nomination to be the U.S. envoy to the United Nations. The Senate Foreign Relations Committee is currently vetting the Bolton nomination, but Cornyn said he doesn’t expect it to affect the bill’s prospects.

“This is a proposal that makes a lot of sense,” the Texas Senator said. “I think the U.S. ambassador to the United Nations is a recognized leader in our government and would be a suitable person to be an acting president.”

The legislation would also abolish the rule that requires a Cabinet officer to resign from office before becoming acting president, and it only permits confirmed Cabinet members to be eligible to serve as acting president.

To rally support for the legislation, Cornyn said he planned to send a letter to individual Senators asking them to co-sponsor it. Sherman said he has spoken to House Judiciary Chairman Jim Sensenbrenner (R-Wis.) and Rep. John Conyers (D-Mich.) about the bill and described them as being “favorably disposed” to it.

In an effort to emphasize the need for Congress to take immediate action, Sherman referred to President Abraham Lincoln’s murder and suggested 21st century terrorists are likely to hatch more intricate assassination plots.

“John Wilkes Booth didn’t just kill Lincoln,” Sherman said of Lincoln’s assassin. “He was the center of a conspiracy to kill the vice president and the secretary of State.

“Osama bin Laden may be even more ambitious,” he added.