The idea of rerunning the UKs historic 52-to-48 percent 2016 vote to leave the European Union is understandably tempting for those in the 48-percent camp. Consider whats happened since: nail-biting negotiations with the EU, polls that showgrowing Brexit remorse, evidence that the UK economy is suffering from the uncertainty the vote has brought. The main UK political parties have both rejected the idea (though Labour Shadow Chancellor John McDonnell refused to rule it out in an interview with Bloomberg TV this week). But that hasnt stopped its advocates at home or even in Europe. Of four recent e-petitions for a new vote, the largest gained 130,000 signatures since September. Manfred Weber, an ally of German Chancellor Angela Merkel and leader of the largest group in the European parliament, spoke on Wednesday of growing UK support for a second referendum. Former Prime Minister Tony Blair, among others, has calledfor a second referendum on several occasions. This week, Welsh Labour Party MP Geraint Davies published a bill that would give voters a choice of whether to accept the final deal that the EU and UK reach. Parliament gave itself a similar choice Wednesday night in a vote that will force the government to submit the final Brexit agreement to its scrutiny before leaving the union, but that may not satisfy remainers bent on a second referendum.  However appealing that course may appear to be, on close inspection the arguments for it are unpersuasive. One weak argument is that voters were lied to by the leave campaign. Its true that there were absurd and misleading claims during the campaign, for example suggesting Britain would reap an immediate financial windfall when it ceased paying membership fees to the EU. Leave voters werent told that the UK would be leaving the single market either. But if democracies reran votes on the basis of specious claims in political advertising, nothing would ever get settled. A stronger argument is based on the fact that voters in the Brexit referendum were comparing a known quantity (EU membership) with an unknown one (life on the outside). They had no way to measure the effect of a divorce. By that logic, Britons should get a chance to vote again once trade relationships are set between the UK government and EU negotiators and citizens could reasonably judge the result. Davies, the Welsh MP calling for a second referendum, says the question that should be put to voters is this: Do you support the governments proposed United Kingdom and Gibraltar exit package for withdrawal from the European Union or should the United Kingdom remain a member of the European Union? Voters could answer either "support the governments proposed exit package" or "remain a member of the European Union." That sounds straightforward, but it isnt. One problem is timing. The UK legally leaves the EU on March 29, 2019. Many experts (though not all) say that Article 50, the EU treaty measure by which Britain gave notice of its intention to leave, can be legally reversed before the withdrawal is final. So if the UK were to back out of Brexit via a second referendum, that vote would need to take place before March 2019. Parliamentary democracies are plodding beasts; meeting that deadline would be some feat. Referendums require legislation and up to a year of lead time to prepare. That means that in the next few months, parliament would have to agree on a referendum, the question, the format and other details. Thats implausible. The Labour Party, which represents many pro-Brexit constituencies, is officially against a second referendum (though it wants to retain close EU ties). The Conservative government, which is negotiating the exit, is obviously opposed. Its hard to imagine the circumstances under which a second referendum would have sufficient parliamentary support in the foreseeable future. Once 2019 rolls around, reversing Brexit becomes even trickier. After the UK has left the EU, it would have to make a new application to rejoin; cue another long negotiation. Voters would in that case be in the same position they were in before the first referendum: They would be asked their view on rejoining the EU without knowing the terms. Even straining to imagine the political climate that could enable such a vote, the chances of Britain re-entering the EU on the same terms it left the bloc are vanishingly small. Bloomberg View