Who won the final Trump vs Clinton US presidential debate showdown?

Hillary Clinton and Donald Trump came face-to-face for the final Presidential debate on Wednesday (19 October), and professional polls say Clinton walked away the winner.

That means she was undefeated in all three debates, according to polling. Clinton edged out Trump 49% to 39% in a YouGov poll surveying 1,503 registered voters who watched the debate. The other 12% claimed a tie.

Another CNN/ORC poll showed Clinton ahead by 13 points with 52% to Trump's 39%. Clinton tweeted early Thursday morning about her streak against Trump.

The results from the first debate were 62% to 27% and the second 57% to 34% according to CNN polls. The network skews Democrat, but both these margins are very large.

Clinton tweeted about her win early on Thursday (20 October) following the final debate before voting on 8 November.

But Trump also declared himself the winner and cited an CSPAN Twitter poll showing him with 70% and Clinton with 30% as evidence of his win. He also cited the Washington Times online poll and a win at NJ.com.

The difference with these polls is that they are all online and voters needed to find them and enter their vote. That can lead to scenarios where members of pro-Trump online communities "manipulate user response polls" by swamping them with votes, according to a study by the Pew Research Center.

The study cites evidence that efforts to skew these polls were made after the first debate in order to show Trump as the winner.

Still, professional polls do have their weaknesses. But "the people who consent to an interview and who cooperate may not be a representative sample of all debate watchers," the Pew research said.

Early polls "have the advantage of capturing reactions quickly, before the opinions of pundits and journalists can begin to form a consensus," it said.

But "the people who consent to an interview and who cooperate may not be a representative sample of all debate watchers," it points out.