Chinese President Xi Jinping wants to take advantage of what he believes is the waning influence of the United States around the world under President Donald Trump, said Nicholas Burns, whose 27-year career in diplomacy spanned both Republican and Democratic administrations.

Xi is consolidating power at a “very consequential” meeting of communist officials being held this week in Beijing, Burns told CNBC on Wednesday. The gathering, the Communist Party Congress, is holding its 19th session. The event happens once every five years.

“Xi is just about to become Xi Jinping the most powerful Chinese leader in 45 years since Mao Zedong [founder of the People’s Republic of China and former chairman of the Chinese Communist Party]; more powerful than the great Deng Xiaoping who ushered capitalism, not really socialism, into China,” said Burns, the U.S. ambassador to NATO and the State Department’s third-ranking official during George W. Bush‘s presidency.

“It’s an affirmation of big changes over the past five years,” said Burns, currently a professor at the Harvard Kennedy School of Government. “China is pushing out very assertively against its neighbors in the South and East China Sea.”

Xi, who became China’s president in 2012 and has since pursued a more aggressive approach to foreign policy, is “openly contesting the power of the United States in the Asia-Pacific region,” he said.

“The Chinese government believes that the United States is weakening … from say in the George H.W. Bush administration when we were all powerful in the world,” Burns argued, describing a perception that the U.S. has been “distracted over the last 15 years by the wars in Iraq and Afghanistan.” Burns also advised the elder President Bush and Bill Clinton.

But Burns said China is underestimating “the power and resilience of the United States.” He called the Trump presidency a “leadership crisis” that won’t last forever, adding “there will be a new administration, perhaps in 2020 or maybe even a little longer.”

Burns was critical of the Trump administration’s nationalistic approach to trade, immigration and key U.S. alliances.

“Our alliances, NATO and the East Asian alliances, that’s the power differential between the United States and China. And the president is weakening those alliances,” Burns contended. “He’s shown us in 10 months what he doesn’t believe in,” not what he wants to accomplish.

However, Burns said the Trump administration is taking the correct approach in putting aside tough trade rhetoric on China in favor of enlisting the world’s second-largest economy to help deal with the provocations of North Korea. There’s been some success in getting China, an ally of North Korea, to apply some pressure, he said.