Acting US Defense Secretary Patrick Shanahan's first full day at the Pentagon's helm was overshadowed Wednesday when President Donald Trump attacked his predecessor Jim Mattis.
Shanahan, who took the Pentagon's top spot January 1 after serving as deputy defense secretary, was thrust onto the world stage when Mattis quit last month amid long-running disagreements with President Donald Trump.
During televised remarks ahead of his first cabinet meeting of 2019, Trump claimed he had "essentially fired" Mattis, even though the former Pentagon chief had pointedly quit his post over multiple disagreements.
"I'm not happy with what (Mattis has) done in Afghanistan and I shouldn't be happy," Trump said, as Shanahan sat by his side.
"I wish him well. I hope he does well. But as you know, President Obama fired him and essentially so did I. I want results."
Mattis, a former Marine general, was head of US Central Command when Obama fired him in 2013 over his hawkish views on Iran.
Soon after arriving at the Pentagon, Shanahan told colleagues to focus on the National Defense Strategy, a Mattis-era review that highlights "Great Power competition" with Russia and China.
"In 2019, the National Defense Strategy remains our guide. America's military strength remains our focus," Shanahan said in a New Year's message on Twitter.
A defense official added that Shanahan had told colleagues a major concern would be China.
"While we are focused on ongoing operations, Acting Secretary Shanahan told the team to remember: China, China, China," the official said.
Little known outside business and Washington circles, Shanahan takes the world stage at a time of tumultuous changes and unpredictable foreign policy moves under Trump.