Story highlights McCain said he would offer an amendment to the National Defense Authorization Act in September

McCain started his treatment for brain cancer on Monday

(CNN) Senate Armed Services Chairman John McCain on Monday threatened to present President Donald Trump with his own Afghanistan strategy if the Trump administration won't develop its own.

McCain issued a statement saying he would offer an amendment to the National Defense Authorization Act in September that would provide a strategy for Afghanistan, the 16-year war that has been a divisive issue within the White House.

"More than six months after President Trump's inauguration, there still is no strategy for success in Afghanistan," the Arizona Republican said. "Eight years of a 'don't lose' strategy has cost us lives and treasure in Afghanistan. Our troops deserve better. When the Senate takes up the National Defense Authorization Act in September, I will offer an amendment based on the advice of some our best military leaders that will provide a strategy for success in achieving America's national interests in Afghanistan."

McCain, who started his treatment for brain cancer on Monday, has long harped on Trump and top national security administration officials to provide Congress with a strategy for Afghanistan, where for years he slammed the Obama administration's timelines for withdrawing US troops from the conflict.

The Afghanistan plan has been delayed for months amidst sharp disagreements between national security adviser H.R. McMaster, who is arguing for an increase of several thousand troops to help turn the tide in the fight against the Taliban, and the President's chief strategist Steve Bannon, who is opposed to getting the US more deeply involved in the conflict.

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