As Donald Trump builds the team he has promised will drain the Washington swamp, the president-elect may temper concerns provoked by early controversial picks by hiring a respected but tough-talking Marine general.

As the Republican billionaire's motley crew of advisors gathered once again Monday at his Trump Tower offices in New York, talk was of retired general James "Mad Dog" Mattis being nominated as secretary of defense.

Despite the 66-year-old Marine's renowned frankness -- "Be polite, be professional, but have a plan to kill everyone you meet" -- he enjoys warm support in Washington and should sail through confirmation.

No immediate announcements were expected, Trump spokesman Jason Miller said, but meetings are scheduled throughout the day.

After Mattis, Trump's other choices may prove more complicated, such as that for secretary of state, reportedly between former Massachusetts governor Mitt Romney and former New York mayor Rudy Giuliani.

Both met Trump over the weekend at the Trump International Golf Club in Bedminster, New Jersey, but no steer emerged as to who will become Washington's top diplomat.

Trump has been no slower than his predecessors to name a cabinet. President Barack Obama, after his 2008 victory, waited until December before naming foreign policy and national security officials.

But the 70-year-old property tycoon is a Washington outsider who vowed to shake up the ruling elite, so some of his choices may find it hard to get past the Senate -- or to obtain a security clearance.

Time may therefore become a factor as the United States counts down to the January 20 transfer of power, and Trump's first nominations last week raised some eyebrows for their past positions.

Trump's pick for National Security Adviser, former head of the Defense Intelligence Agency Mike Flynn, had obviously enjoyed high-level clearance until Obama forced his early retirement in 2014.

But he has since accepted hospitality from Russia's President Vladimir Putin and taken lobbying work from a firm reportedly close to Turkey's President Recep Tayyip Erdogan, so he may face new questions.

The National Security Advisor role is in the gift of the president -- so Flynn does not need Senate approval -- but he will need to pass an FBI background check to restore his security clearance.

- Sensitive post -

As a serving senator, Trump's choice to lead the CIA, Mike Pompeo, might expect an easy ride at the hands of his former colleagues, tasked with vetting his suitability for the sensitive post.

But he has argued that US spy agencies need unrestricted powers to collect data online from both US citizens and foreigners and has defended the CIA's former use of torture on detainees.

Republican Senator John McCain, himself a torture victim as a prisoner of war in Vietnam, said at the weekend: "I don't give a damn what the president of the United States wants to do... We will not torture people."

Another leading Republican, Senator Rand Paul, opposes domestic surveillance and has concerns about two possible Trump picks: Giuliani and neo-conservative former diplomat John Bolton.

- Execution of a Klansman -

In television interviews on Sunday, Paul said he would want to hear from any secretary of state nominee that the 2003 US invasion of Iraq -- which Giuliani and Romney supported -- was a mistake.

Trump's pick for attorney general, Senator Jeff Sessions, ought not to face stiff resistance from his Republican colleagues, but his record on race and civil rights has stirred a political storm.

Kellyanne Conway, Trump's campaign manager, was staunch in her defense of all the nominees and potential nominees, and dismissed allegations that Sessions' record marks him as a racist.

As attorney general of Alabama, Conway told CNN, he supported the execution of a Klansman -- "The first time a white man was given the death penalty for killing an African-American man in Alabama since 1913."

Later, as a US senator, Sessions voted to confirm the appointment of Obama's attorney general Eric Holder, another African American.

Conway would not be drawn on whether Giuliani or Romney will be secretary of state: "They both have been very distinguished public servants."

- Meets a Democrat -

Giuliani has been Trump's most loyal champion, the first on air to defend him after footage emerged of the tycoon boasting that he groped women with impunity.

In contrast, Romney was Trump's most outspoken Republican critic during the race, branding him a "phony" and a "conman" who would destroy his party and bring shame on his country.

Trump began his latest series of hiring meetings on Monday with a Democrat, Hawaii Representative Tulsi Gabbard, who is reportedly being considered for a foreign policy position.

Late on Tuesday or early on Wednesday, Trump is to fly to his Mar-a-Lago resort in Florida to take a "brief" Thanksgiving holiday Break with his family, his team told reporters.

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