Retired Gen. James Mattis heads to Capitol Hill Thursday to be grilled by the Senate Armed Services Committee for his confirmation as secretary of defense.

At stake is control of the Pentagon, one of the most crucial positions in the Cabinet that will determine whether President-Elect Donald Trump is able to deliver on promises to rebuild the military and combat a slew of international threats.

“It’s not Trump that causes the Baltics to quake. It was eight years of Obama.”

The armed forces face many challenges — including a more aggressive Russia, a more aggressive China, an Iran that can’t seem to shake its fondness for terrorism, and aging equipment.

President Obama also oversaw a steady decline in the number of combat-ready troops in his eight years, leading his own secretary of the Army, John McHugh, to declare the Army was at “the ragged edge of readiness” in October 2015. Trump has also indicated he believes the military’s complaints that nuclear equipment is aging and in need of upgrades and replacement.

Complicating matters for Mattis is the fact that the four-star general retired only three years ago.

[lz_ndn video= 31696304]

Under federal law, a retired military veteran has to wait seven years before heading up the Pentagon. The law was passed to enforce an unwritten rule about civilian control of the armed forces.

Before Mattis, the last high-ranking officer to hold the office was Gen. George C. Marshall, the five-star general who served as the top Army official under Franklin Roosevelt and Harry Truman. Marshall took the job in 1950.

Marshall had to get a waiver from Congress, which passed a 10-year rule in 1947. The Congress reduced the wait time to seven years in 2008.

The principle wouldn’t be violated by Mattis, who has been out of uniform since 2013. But some Democrats oppose a congressional waiver. And without it, Mattis is the only Trump Cabinet nominee whom Democrats could actually block along a strictly party-line vote.

Who do you think would win the Presidency?

By completing the poll, you agree to receive emails from LifeZette, occasional offers from our partners and that you've read and agree to our privacy policy and legal statement.

Some Democrats jumped early to oppose Mattis.

“While I deeply respect General Mattis’s service, I will oppose a waiver,” said Sen. Kristin Gillibrand (D-N.Y.) in a statement last year. “Civilian control of our military is a fundamental principle of American democracy, and I will not vote for an exception to this rule.”

To get that waiver, Mattis was to meet on Thursday with the House Armed Services Committee, but he canceled on Wednesday, perhaps not to step on the Senate’s famously sensitive toes.

But his service — ironically, the biggest issue in his confirmation hearings — isn’t the only issue that will likely come up today, according to experts.

Michael Rubin, a resident scholar the American Enterprise Institute and a former Pentagon official, said he doesn’t expect the hearings to be contentious, but he does expect lots of questions.

For one, when Mattis served in the Iraq War, he lost a lot of soldiers to Iranian terrorists, who supplied explosives to Iraqi insurgents. Mattis also reportedly opposed Obama’s nuclear deal with Iran.

Israel is also a sore spot for Mattis skeptics, albeit a small one.

After he retired, Mattis told CNN that when he was head of the U.S. Central Command, allied nations perceived him as “biased in favor of Israel.”

“I paid a military security price every day as the commander of CentCom because the Americans were seen as biased in support of Israel, and that moderates all the moderate Arabs who want to be with us, because they can’t come out publicly in support of people who don’t show respect for the Arab Palestinians,” Mattis told CNN.

[lz_related_box id=”270100″]

His comments have not drawn the type of criticism that drew trouble for Sen. Chuck Hagel (R-Neb.) the former secretary of defense who underwent rocky hearings in 2013. Hagel, however, had lobbed much more criticism the way of Israel in his career.

Other issues, Rubin said, could be U.S. troops in Syria, defense spending, budget constraints, massive Pentagon bureaucracy, and Chinese aggression.

But look for Democrats to make hay out of Mattis’ perceived differences with Trump on Russia. Mattis supported NATO readiness in case Russia got aggressive with the Baltic states, such as Estonia.

Trump is perceived as being soft on support for NATO allies in Europe.

Robert Kaufman, Dockson professor of public policy at Pepperdine University, said the contradictions aren’t that deep.

Kaufman said the problem with readiness to protect Eastern Europe was one caused by Obama, not Trump. Under Obama, military support of NATO weakened in Eastern Europe, giving Putin a growing advantage.

“It’s not Trump that causes the Baltics to quake,” said Kaufman. “It was eight years of Obama.”