The president of the United States on Wednesday sought to distance himself from the defeat suffered by a controversial Republican candidate in a special US Senate election in Alabama.

The loss sustained by 70-year-old Judge Roy Moore, whose campaign was marred by allegations he preyed upon teenage girls several decades ago, shrinks the Republicans' slim majority in the US upper house of Congress to 51-49.

"The reason I originally endorsed Luther Strange (and his numbers went up mightily), is that I said Roy Moore will not be able to win the General Election. I was right! Roy worked hard but the deck was stacked against him!" Donald Trump tweeted Wednesday morning.

The Democratic candidate, attorney Doug Jones, obtained 49.9 percent of the vote in Tuesday's balloting to barely beat out Moore, who garnered 48.4 percent with all precincts around the state counted.

Moore has refused to concede pending a tallying of overseas ballots, although Jones' margin of victory is currently above the range of between 0 and 0.5 percentage points that would trigger an automatic recount.

Moore won the Republican primary in Alabama in a surprise over Trump's favored candidate, Luther Strange, who was appointed interim senator when Jeff Sessions stepped down in January - two years into his six-year term - to become Trump's attorney general.

But after becoming the GOP's nominee, several women came forward alleging Moore had sexually abused or made unwanted sexual advances toward them.

Most of the accusers were minors at the time the alleged incidents occurred; three say that Moore sexually abused them, with two of those purported incidents occurring in the late 1970s and the other in 1991.

Moore has given evasive answers in interviews when asked whether he dated teenage girls when he was in his 30s, but he has denied the sexual misconduct allegations.

Despite the accusations, Moore was strongly backed by members of the populist wing of the Republican Party - including Trump's former chief strategist, Steve Bannon - who thought he would be a reliable supporter of Trump's America First agenda.

Establishment Republicans, however, were much more lukewarm on his candidacy.

Senate Majority Leader Mitch McConnell called on Moore to drop out of the race after the accusations were leveled, although he later said the people of Alabama should be allowed to make their decision at the ballot box.

House Speaker Paul Ryan said prior to the election that Moore should have pulled out due to the multiple allegations.

Even before the accusations surfaced, Moore, an evangelical Christian, was a controversial figure who was twice suspended from his position as chief justice of the Alabama Supreme Court for refusing to uphold federal law due to his religious beliefs.

Although Trump did not initially support Moore's candidacy, some pundits have concluded that the latter's defeat is a sign of diminishing support nationwide for the president.

Trump handily won Alabama in the 2016 presidential election.