The stakes are high for the NATO alliance as the organization's 75th anniversary summit gets underway in Washington this week.
Particular focus will be on U.S. President Joe Biden amid widespread concerns about his age and mental fitness for the presidential race following his damaging debate performance against former President Donald Trump in June.
Former NATO Deputy Secretary-General Rose Gottemoeller stressed this point in a discussion with CNBC's "Capital Connection" on Tuesday.
"I think this NATO summit in Washington is an important moment for Joe Biden, he really has to show that he is with it, he's ready to continue to lead not only the United States of America but the NATO alliance," she told CNBC's Dan Murphy. "And so we will see in coming days just how well the U.S. president does."
Asked if the summit could be make or break for the trans-Atlantic alliance, Gottemoeller replied: "I think it is an extraordinarily important summit for the NATO alliance; I wouldn't say it is a make or break. NATO has had many ups and downs over the years and some severe crises to deal with ... it's a difficult moment for NATO, but NATO has weathered a lot of crises before."
The alliance's main focus is currently supporting Ukraine in its war with Russia, an effort that many in the organization fear could be in peril if Trump wins the American presidency in November.
The U.S. supplies the lion's share of financial and military support to Kyiv, and Trump has for years threatened to pull the U.S. out of the alliance if he returns to the White House. He has also expressed opposition to continuing to send military aid to Ukraine.
"I'm not predicting necessarily a Trump win in November; nevertheless, there will be tremendous pressure on the alliance I think from Donald Trump as there was during his first term in office when I was serving as deputy secretary-general at NATO," Gottemoeller said. "He was unrelenting in pushing the NATO allies to spend more on their own defense."
Trump routinely threatened member countries that did not meet the NATO requirement of spending 2% or more of their gross domestic product on defense. He said in a February campaign rally that he would let Russian President Vladimir Putin attack member states that did not spend enough on their defense.
But Trump will "see a much different NATO" if he wins a second term, Gottemoeller said. "I think he was important in getting the momentum going, getting NATO to spend more on its own defense," she said, but emphasized that in the face of Putin's full-scale invasion of Ukraine, member states have been stepping up significantly.
When Trump was in office, fewer than 10 member states were spending 2% of their GDP or more on defense and that figure has risen to 23 out of the alliance's 32 current members, Gottemoeller said.
Gottemoeller, who currently lectures at Stanford University, expressed skepticism that Trump would actually withdraw from NATO, despite his threats on the campaign trail. Still, it will be "very, very important for the NATO allies to be paying close attention to Trump and what he wants to accomplish" should he win, the former diplomat said.
If Trump returns to the White House, a "core demand" will be for NATO allies to spend more than 2%, she said. "We already heard that during his first time in office, and I think we will hear it again."
Gottemoeller served as NATO's deputy secretary-general from 2016 to 2019 and on the White House's National Security Council as director for Russia, Ukraine and Eurasia affairs in the early 1990s. She was later was undersecretary of State for arms control and international security at the State Department.