Democrat Senator Chris Coons, who represents ocean state Delaware which has strong links to the US Navy and US Air Force, warned: “We can ‘lose’ and we can lose decisively.”
Mr Coons was speaking at the think-tank Royal United Services Institute in London and raised concerns over the state of NATO and that he is “determined” to ensure ties remain strong between the United States and the alliance, despite “obvious current strains”.
He also explained how NATO is a “key institution” against countries like Russia and China.
The senator criticised President Donald Trump’s plans to withdraw troops from Syria and Afghanistan – a decision which has been criticised in both the US and the UK.
President Trump claimed the so-called Islamic State group were “doomed” last year as he announced troops would pullback from Syria.
But despite the defeat of IS edging closer, experts have been concerned over what a US withdrawal could mean.
One expert told Forces News that a fast US withdrawal, which President Trump originally wanted, could create “a security vacuum” in the country for IS.
“A hasty withdrawal, a hasty and complete withdrawal as recently proposed by our President in the United States would threaten the military progress and the socio-economic progress made,” explained Mr Coons.
“I think our withdrawal would encourage both Russia and Iran in Syria and leave civil strife and space for terrorist groups.
“A comparable withdrawal and a comparable timeline, which hasn’t yet been prosed but I feel is imminent, would have the same consequences in Afghanistan.
“I’m not saying our troops should stay in Afghanistan or Syria forever… but the presence of US and allied troops prevents safe havens for terrorists.
“There is not a high likelihood of a clear-cut military battlefield victory in either conflict.
Mr Coons admitted the terrorist threat remains despite the advances made by the US, the UK and other allies.
He said US presence can prevent terrorist groups from “establishing large physical strongholds” and it is better to “fight them [terrorists] over there so we don’t have to fight them over here”.