As many as 30 Republican members of the Electoral College are willing to break their pledge and vote against Donald Trump in order to block him from becoming the US President, according to a Harvard University law professor.

Larry Lessig, who was himself briefly a candidate for the 2016 Democratic nomination, has been offering legal support to electors on their right to “vote their conscience” - that is, to reject the mandate given to them by the winner of the popular vote in their specific state.

Most states bind their electors to the popular vote by state law, but Mr Lessig said there was precedent to say these are federal officials, granted powers by the federal constitution, who should “be able to exercise their independent and nonpartisan judgement about who to vote for”.

So far only one Republican elector, Chris Suprun of Texas, has come out publicly and said he will not vote for Mr Trump when the Electoral College meets on 19 December, describing the President-elect as unqualified to lead.

But speaking to MSNBC on Tuesday night, Mr Lessig said many more were privately considering their options - and if the number gets close to the 37 needed to stop Mr Trump reaching the 270 target, “there will be a very interesting dynamic”.

“Surveying the three groups that are supporting Republican electors, we believe there are 20 right now - some tell me the number is higher than that, it should be more like 30 - but I feel confident in saying there’s at least 20,” he said.

While Mr Trump is more than 2.8 million votes behind Hillary Clinton in the nationwide popular vote, he won a clear victory in the Electoral College system that most people now expect to simply rubber-stamp the result.

Mr Lessig argues that the Electoral College was not created by the founding fathers as just a cog in the machine, however, describing it as “the emergency brake on the process of selecting a president”.

Electors “have an ethical, moral obligation once they take the pledge… [to] vote [with their state] unless there is an overriding moral reason not to vote that way. The failure of a candidate to live up to the qualifications would be one such reason", he said.

“And thats exactly the issue raised by this election, the Electoral College was made for this election precisely.”

Never in the history of US presidential elections has the Electoral College as a whole blocked the result of the public vote. The closest it came was in 1808, when six Democratic-Republican electors rejected James Madison.

Asked why this year is different, Mr Lessig said: “Reasons like the threat of foreign involvement in our election, or a candidate who refuses to live up to the foreign bribery (Emoluments) clause by disassociating himself or divesting himself from assets that could be affected by foreign governments.”

Mr Lessig has provided no evidence for his assertion that between 20 and 30 Republican electors are considering voting against Mr Trump, and the Republican National Committee said its own whip operation to reach out to electors found only one - Chris Suprun - willing to go rogue.

If 37 faithless electors could be found, it would still be a long way from stopping Mr Trump becoming President eventually. In the event that the Electoral College cannot provide a candidate with the 270 votes needed for a majority, the Constitution dictates that the decision goes to Congress.

Congress would be asked to choose a victor from the most successful three candidates, assuming the faithless electors put down a third option such as John Kasich, as Mr Suprun has pledged to do.

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“Congress would have to weigh the reasons that raised this issue and make a decision one way or another,” Mr Lessig said. But he also notes that Republicans “actually have an advantage in that situation” anyway, because the Constitution rules that each state gets one vote, and there are many more Republican states than Democratic states.

In other words, even in an ideal scenario his efforts are almost certain to fail - and if they succeeded, it would likely see violent unrest on the streets. So why is he doing it?