Donald Trump cast himself both as a peacemaker and fierce defender of US interests in a mercurial return to the White House on Monday, vowing to seize the Panama Canal but also imploring Russia to make a deal on Ukraine.

Newly sworn-in President Donald Trump vowed on Monday that the United States would take back the Panama Canal as he delivered an inauguration speech in which he invoked the 19th century expansionist doctrine of "Manifest Destiny" in laying out plans for space exploration.

Donald Trump argues that the US needs Greenland for national security, while a retaking of the Panama Canal is necessary to curb the overcharging of American ships and combat Chinese influence.

Rep. Dusty Johnson told reporters Friday that he wants to give President-elect Donald Trump the option to pursue the purchase of the Panama Canal.

Trump has repeatedly threatened to take ownership of the critical maritime trade route — which the U.S. signed over to Panama in 1977 — calling it “vital” to American interests and refusing to rule out using military force in pursuit of his goal.