U.K. Prime Minister Boris Johnson appears to be steaming toward the parliamentary majority he desperately desires to pass his Brexit deal and end the gridlock in Westminster.Why it matters: Thursday’s vote is the culmination of three years of intense efforts to deliver Brexit, and to block it. The rocky road Johnson has plodded along since replacing Theresa May in July would become much smoother with a resounding electoral mandate.Driving the news: This has been a brutal campaign fought by two leaders who are disliked and distrusted by broad swaths of the public.Johnson has been accused of repeatedly misleading voters, while opposition leader Jeremy Corbyn has been charged with allowing anti-Semitism to fester within his Labour Party.Opponents of Brexit now believe the only thing that can stop a Johnson majority is tactical voting, with voters selecting Labour or the fiercely anti-Brexit Liberal Democrats depending on which party is more likely to defeat the local Conservative candidate.The latest polls:Conservatives: 43% (+5 since election called in late October)Labour: 33% (+7)Lib Dems: 13% (-3)Brexit: 3% (-7)Greens: 3% (=)Breaking it down: James Johnson, who ran Downing Street’s polling under Theresa May, gives the Conservatives a 75% chance of a parliamentary majority.If they fall short, one scenario would see Labour form a coalition with the Liberal Democrats and the Scottish National Party.That could put Corbyn into Downing Street and lead to second referendums on Brexit and Scottish independence, which voters rejected in 2014.Numbers to watch: Johnson's bar for success is the 326 seats needed for a majority, though he might keep the top job if he falls just short.Johnson, the pollster, adds that the prime minister is aiming to best the 330 seats David Cameron won in 2015. That would mark the biggest Conservative majority since 1992 and also constitute a triumph in his long-standing rivalry with Cameron, his old schoolmate.Corbyn's survival as Labour leader will likely depend on denying the Conservatives a majority, Johnson says.“There’s a real sense in Westminster that he’s keen to jump ship,” he notes, adding that it would likely be a managed transition within the party’s leftist faction: “Corbynism doesn’t die with Corbyn.”The big picture: Johnson has based his campaign on the argument that if the U.K. can only “get Brexit done,” it will be able to move onto other things, including a great new trade deal with the U.S.Reality check: Peter Westmacott, a former U.K. ambassador to Washington, says even if Johnson’s Brexit deal passes, there will be “numerous dramas throughout the course of 2020” as the U.K. negotiates its future trading relationship with the EU, while a U.S.-U.K. trade deal will take “years of hard bargaining."“We’ve got an America-first, unilateralist, protectionist president of the United States. It’s not going to be easy,” he says.