Sen. John McCain (R-Ariz.) is chairman of the Senate Armed Services Committee. (J. Scott Applewhite/AP)

Sen. John McCain on Thursday unveiled a plan to increase U.S. air and ground forces in Afghanistan that would probably bring some American soldiers closer into harm’s way — a move that in effect rebukes President Trump, who has not yet decided on his preferred way forward in the war.

McCain (R-Ariz.) promised to present his plan as an amendment to the annual defense authorization bill, upon his return to Washington in September.

The senator is undergoing treatment for a recently diagnosed brain tumor, but congressional Democrats and Republicans alike have said they will change the Senate schedule to ensure that McCain, the chairman of the Senate Armed Services Committee, is able to steer the huge $700 billion measure.

McCain has not shied away from crossing Trump on key policy issues. Last month, he voted against the health-care overhaul bill, effectively ending the chances to pursue a “repeal and replace” measure in the Senate. And since last year, McCain has consistently excoriated Trump for not taking more seriously the threat of Russian meddling in U.S. elections.

But Afghanistan is a particularly troubling issue for McCain, who has long been impatient with the White House for not providing a cohesive strategy for its combat operations in the war-torn country. For eight years, McCain railed against the Obama administration for the lack of a satisfactory plan, and the senator has warned the Trump administration that if it failed to articulate something better than “a ‘don’t lose’ strategy,” he would try to force the president’s hand by demanding a vote on a plan as part of the defense bill.

(Jenny Starrs/The Washington Post)

On Thursday, McCain apparently lost his patience.

“Nearly seven months into President Trump’s administration, we’ve had no strategy at all as conditions on the ground have steadily worsened,” he said in a statement released along with the plan. “We must face facts: we are losing in Afghanistan and time is of the essence if we intend to turn the tide.”

Trump has also been frustrated with the protracted war in Afghanistan but has been sitting on proposals from the Pentagon to increase troop levels as he wrestles with his two priorities: to win the war in Afghanistan to get U.S. troops out as quickly as possible.

On Thursday, he told reporters at his golf club in Bedminster, N.J., that “we’re getting very close” to articulating a strategy for Afghanistan. “I took over a mess, and we’re going to make it a lot less messy.”

He also suggested he continues to support his national security adviser, H.R. McMaster, despite pressure from conservative activists to fire him and reports that Trump might make him the next commander of operations in Afghanistan.

“He’s my friend, and he’s a very talented man,” Trump said. “I like him, and I respect him.”

What cleaning up Afghanistan means in terms of committed troop numbers in the short and long term, however, is not yet as clear as it is in McCain’s proposal. McCain’s plan outlines short- and long-term goals that envision a significant U.S. presence on the ground — an approach “to ensure that Afghanistan never again becomes a sanctuary for terrorists to plot and conduct attacks against America.”

McCain does not outline specific troop numbers. But among his plans is a proposal to integrate U.S. military training and advisory teams at the battalion level of the Afghan armed forces known as “kandaks” — each of which has about 600 troops in it. That commitment would by necessity raise the number of U.S. forces in Afghanistan significantly and put those troops — even in their advising and training roles — closer to combat.

McCain’s plan also envisions more U.S. air power and combat support for the Afghan military, and expects that “in the long term” the United States will provide “sustained support” for those troops, even as Afghan forces become more self-sufficient.

Thomas Gibbons-Neff and Dan Lamothe contributed to this report.