WASHINGTON: Of all the areas where Barack Obama and Sen. John McCain clashed during the 2008 presidential campaign, none was more combustible than defence, with their starkly different views on the deployment of American men and women to wage war overseas.

Now, McCain is expected to assume the chairmanship of the Senate Armed Services Committee, with its congressional purview over all things national security, including the Pentagon budget and President Barack Obama’s prosecution of the war on Daesh.

The White House is already expecting trouble. “We have no doubt that Senator McCain will be a formidable adversary as chairman of the Armed Forces Committee,” a senior administration official said last week. He added a hopeful note, saying the White House was ‘certain’ the two men would be able to ‘construct a constructive’ relationship.

But in just the last five months, McCain, R-Ariz., has called for the president’s entire national security team to resign, accusing it of failing to keep Iraq secure. McCain has insisted that US ground troops must be sent into Syria and Iraq to fight Daesh, calling Obama’s air-strikes-only strategy ‘a disaster’. And he has accused the White House of churning out ‘spins and lies’ in defence of its military campaign plan for Iraq and Syria.

Now, with the gavel of the powerful Armed Services Committee almost certain to come into his hand, McCain will have a bully pulpit, accompanied by a megaphone.

He will be able to schedule hearings in which the US generals conducting Obama’s military campaign in Iraq and Syria may be exhorted to say whether they really do think Daesh can be defeated without the use of US combat troops, as the White House still maintains. (Many do not.)

McCain will also be better able to use nominations, administration legislative proposals and programs as leverage to prod Obama toward his own views.

“I want the committee to be very active,” McCain said in an interview after the midterm elections set up Republican control of both houses of Congress. “That’s the beauty of the majority, as you know. Of course we can allocate and authorise certain programs, and we can cut others. The president proposes, and Congress disposes.”

Obama, as commander in chief, still has the final say in whether US ground troops will be committed to Iraq and Syria; whether the United States will do more to arm moderate rebels in Syria opposed to the government of President Bashar Assad; or even whether the United States will take a more muscular posture against Russia’s president, Vladimir Putin, over Ukraine.

“There is one commander in chief,” said Roger Zakheim, a former general counsel for the House Armed Services Committee’s Republican leadership, who is a visiting fellow at the American Enterprise Institute. “Having said that, you can drive debates when you have the gavel.”

Zakheim said the Senate Armed Services chairman “has the authority to call hearings and drive investigations and to promote and shape policies he thinks are necessary.”

At the top of his agenda, McCain said, will be looking to repeal across-the-board budget cuts, called sequestration, for the defence department.

But that effort may pit defence hawks among Republicans against deficit hawks in their own party. And while McCain is unabashedly among the defence hawks, there are some high-dollar weapons systems he may challenge to prove their value. So he has made clear that even his ascent to chairman of the Armed Services Committee does not mean an open spigot on military spending.

He said he intended to work toward reforming how the defence department buys the weapons and technology the US military needs. And he has been outspoken in his criticism of the F-35 fighter jet, which has suffered a number of delays and cost overruns. He is also sharply critical of the Navy’s littoral combat ships, a new class of vessels that can operate on the ocean and in shallow coastal waters, but cost more than $700 million (Dh2.57 billion) apiece.

McCain said recent Pentagon acquisitions had been subject to far too many cost overruns. He specifically mentioned the Gerald R. Ford, the lead ship in the Navy’s next class of nuclear-powered aircraft carriers, which is over budget.

“The USS Gerald Ford was supposed to cost $10 billion, and ended up costing $13 billion,” McCain said. “I can’t tell you the number of things the state of Arizona could do with $3 billion. We lose our credibility when we advocate for increased defence spending, and we don’t hold anyone responsible.”

He said he planned to dedicate specific Armed Services Committee staff members solely to looking into defence department acquisitions.

“A McCain chairmanship will incentivise the defence industry not to make mistakes,” said Loren B. Thompson of the Lexington Institute, a policy research organisation, who has also done consulting work for the defence industry. “His criticisms are always grounded in some truths.”

Thompson added that “people remember how he mauled the F-35,” but he said many of McCain’s critiques had led to changes in the programme.

McCain sounded upbeat about tangling with the weapons industry on acquisitions. “I can assure you, they’re not thrilled about my becoming chairman,” he said with a chuckle.

Of course, McCain has not officially been named to the chairmanship yet, but he said he expected to be given the job by his Senate colleagues. He is more senior than the committee’s current ranking Republican, Sen. Jim Inhofe of Oklahoma, who is expected to become chairman of the Environment and Public Works Committee.