Donald Trump deletes tweets urging support for Luther Strange

US president Donald Trump threw his support behind Luther Strange in Alabama, but has since deleted tweets expressing his support. Photo / AP

US President Donald Trump's command over Republicans has been called into question after his preferred candidate in an Alabama primary was defeated.

The billionaire, who has boasted about only backing winners, deleted all tweets where he supported Senator Luther Strange to take Jeff Sessions' seat, after the Republican became Attorney-General.

Populist candidate Roy Moore won the primary run-off with the support of Trump's former chief of staff, Steve Bannon, who had been campaigning for him.

BothTrump and Vice President Mike Pence travelled to Alabama to campaign for Sen Strange but it wasn't enough.

pic.twitter.com/NQYY0IL50d

— Burgess Everett (@burgessev) September 27, 2017

The race had been seen as a barometer of Trump's political persuasion.

The president has deleted tweets before but generally only when he makes spelling mistakes.

On Tuesday morning, Trump had tweeted: "ALABAMA, get out and vote for Luther Strange - he has proven to me that he will never let you down! #MAGA"

Earlier in the morning, Trump had tweeted: "Luther Strange has been shooting up in the Alabama polls since my endorsement. Finish the job - vote today for 'Big Luther.'"

US vice president Mike Pence, right, was also hauled in to support Luther Strange, who lost the Alabama primary. Photo / AP

On Monday night, Trump had tweeted: "Big election tomorrow in the Great State of Alabama. Vote for Senator Luther Strange, tough on crime & border - will never let you down!"

All three have now been deleted.

The question has also been raised whether Trump is violating the Presidential Records Act of 1978, which requires all the president's records be preserved for eventual release to the public on a delayed basis long after the commander in chief leaves office.