Truss only took over from former leader Boris Johnson on September 6 after winning an internal Conservative Party leadership contest in early September.
President Biden thanked Liz Truss for her partnership on the Russia-Ukraine conflict after the embattled PM dramatically quit Thursday after just six weeks on the job.
After Ms Truss embarrassingly quit this afternoon after a mere 44 days in power, the party announced would-be successors would need to win the support of 100 MPs to get on the ballot.
The Prime Minister had been texting friends late into the night after a chaotic day in Westminster which saw her sack her home secretary and then plead with her Chief Whip not to resign hours later.