The tide appears to be turning against Donald Trump, following Roy Moore's loss in Alabama.

The Republican candidate narrowly lost to Democrat Doug Jones, after facing allegations of sexual misconduct.

The US president has been heavily criticised for continuing to endorse Moore.

READ MORE: Jones's stunning upset win a blow for Trump

CNN Political Editor Mark Preston said the harshest criticism has come from the Republican establishment and more conservative media like USA Today.

"What this shows is the erosion of Donald Trump's support, not only from his supporters but the willingness from the media and others to give him some breathing space."

Jones' victory will narrow the Senate Republican majority to 51-49 which Preston said will make it harder for Trump to get anything done in the next 12 months.

"Of the 51 Republicans, there are a handful that are considered 'squishy Republicans', in the sense that they tend to be a little more centrist [and] do not necessarily toe the party line," Preston said.

Trump is defending his decision to initially back Senator Luther Strange against Roy Moore in Alabama's senate election.

"I was right!" the president said in a pre-dawn Twitter post on Wednesday, a day after Democrat Doug Jones narrowly defeated Moore, a former state Supreme Court chief justice who was buffeted by allegations of sexual misconduct.

He noted in his social media post that the reason he originally sided with Strange was that "I said Roy Moore will not be able to win the General Election."

Trump also added: "Roy worked hard but the deck was stacked against him."

The president had sent a tweet late Tuesday congratulating Jones, a former federal prosecutor, on his "hard fought victory."

Jones's term lasts until January 2021.

- additional reporting, AP

Doug Jones' victory in Alabama means that Democrats are only two seats away from the majority. While a Democratic move into the majority still looks like a long shot, it's now not out of the question.