Washington DC - President-elect Donald Trump's nomination of Pete Hegseth to run the Defense Department was teetering Wednesday as Republican senators raised questions over the Fox News host's fitness for the role.

Hegseth is under intense pressure over a series of misconduct allegations, including accusations of alcohol abuse and a sexual assault claim from 2017, over which no charges were filed.

The former Army National Guard officer denies all wrongdoing, but the controversy has left Trump's transition officials scrambling to avoid the embarrassment of a second Cabinet nomination collapsing amid dwindling support from Republicans in Congress.

Up to six Senate Republicans – including South Carolina's Lindsey Graham, one of Trump's staunchest allies on Capitol Hill – have voiced doubts over Hegseth's ability to walk the confirmation tightrope, according to NBC News.

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The questions around Hegseth's character deepened as an old email emerged in which Hegseth's own mother called him an "abuser of women."

"I think some of these articles are very disturbing," Graham told CBS News of the media coverage around the nomination. "He obviously has a chance to defend himself here, but some of this stuff is going to be difficult."

Republicans will have 53 seats in the incoming Senate majority, meaning Trump's nominees can afford to lose the support of only three Republican votes at their January confirmation hearings, assuming all Democrats vote against them.

Various alternatives have been reportedly floated, with Trump said to be mulling one-time Republican primary rival and Florida Governor Ron DeSantis, despite their bitter presidential nomination battle that only ended with a token reconciliation.

Hegseth was due on for further meetings Wednesday with influential Republicans on Capitol Hill, as well as a TV interview on Fox – his first since being nominated.