Senate Minority Leader Mitch McConnell has written in a new opinion piece that President-elect Donald Trump will “inherit a world far more hostile to U.S. interests than the one he left behind for four years” — and to respond appropriately To respond, he warns Trump that he must reject the isolationism advocated by some in both parties, build economic and military ties with allies and increase spending on U.S. “hard power.”

McConnell, who is leaving his leadership post at the end of the year, has made clear that he will continue to be a voice of opposition to Trump, both on issues of America’s strength around the globe and at home.

In the next Congress, he will chair the Appropriations Committee’s defense subcommittee and have significant influence on military spending issues. And just last week, McConnell, himself a polio survivor, strongly warned the incoming Trump administration against engaging with polio vaccine skeptics.

“Trump would be wise to build his foreign policy on the enduring cornerstone of U.S. leadership: hard power. To reverse the neglect of military strength, his administration must commit to significant and sustained increases in defense spending, generational investments in the defense industrial base, and urgent reforms to accelerate the United States’ development of new capabilities and the number of allies and partners to expand “access to them,” he said.

McConnell called the nearly $900 billion the U.S. spends on defense each year “not nearly enough,” especially because about 45 percent of it goes to salaries and benefits. “The situation is serious,” he said.