Biden's national security team team says he's up for 4 more years

July 20 (UPI) -- President Joe Biden 's national security advisers say he's up to the job while former officials cast doubt on his ability to protect his legacy from Donald Trump .

National security adviser Jake Sullivan, Secretary of State Antony Blinken and Joint Chiefs Chair C.Q. Brown at this week's Aspen Security Forum in Colorado insisted Biden is fully capable of steering the United States through a global landscape marked by fears of Russian and Chinese aggression.

"I am damn glad we have that guy sitting at the head of the table in the Situation Room," Sullivan said Friday in a press conference.

It's rare for national security officials to voice their opinions about domestic partisan politics, but growing Democratic concerns about Biden's fitness for office topped with the recent assassination attempt on Trump has made the topic virtually inevitable in national security discussions.

Sullivan, when pressed about Biden's acuity, pointed to his alert and engaged response to Iran's April 13 missile attack on Israel, which the United States helped fend off.

At that time, "you get to see in living color, in real time, the capacity of a commander-in-chief," Sullivan said.

Brown echoed Sullivan's testimony, saying "all the times I've been engaged with the president, he's been engaged."

But officials who previously sat in their roles were not optimistic about Biden's aptitude for a second term.

In a letter obtained by CNN , 56 former national security officials urged Biden to step down from the race arguing his potential loss to Trump could pose a risk to national security.

"With the deepest appreciation for your many decades of inspired leadership, we strongly believe that ongoing concerns surrounding your continued candidacy and the growing likelihood of an electoral college victory for Donald Trump put your national security accomplishments -- and our country and your legacy -- at an unacceptable level of risk," the letter read.

"Donald Trump's vision, approach and expressed intentions concerning our nation's security are in fundamental conflict with the values and principles for which you have stood."

The letter, which included signatures from officials who served in multiple administrations, was front-lined by John Shattuck, former U.S. ambassador to the Czech Republic, and Eric Schwartz , a former National Security Council official under President Bill Clinton .

The Biden campaign responded to the letter by saying, "this is a time to unify against the national security threat that is Donald Trump. Joe Biden's strong and steady leadership are essential at a time when dictators and despots around the world are threatening established norms, laws, and borders.

His experience and knowledge in foreign affairs is unmatched - that is exactly it is essential he win this November."