|John Kasich celebrates victory in his home state of Ohio last night|
Nevertheless, Trump's ability to win the support of white, working-class conservatives will not be enough to propel him to the White House. His populist message may resonate amongst disaffected blue collar voters - the so-called 'losers' of globalisation who feel exploited by America's political and financial elites - but in the general election we will soon see the limits of Trump's candidacy. Whilst the Republican Party has responded to two presidential defeats by moving towards inhospitably extreme positions and surrendering the intellectual high-ground to the hard-right, America has embraced modernity and all that comes with it. The GOP will never win the White House again until it reflects these changes and espouses a more inclusive platform.
For mainstream Republicans, this presidential campaign has been nothing less than agony. GOP primaries are usually characterised by a whole host of eccentric and hardline candidates lining up to (unsuccessfully) challenge the establishment frontrunner, but this year has seen a complete inversion of that traditional model as favourites of the party's mainstream wing have come and gone, only to be swatted away by the seemingly indomitable Donald Trump.
First up was Chris Christie, touted years ago as the one to watch in this election cycle, but the New Jersey governor's tough-guy persona failed to gain traction and by the time of the first Republican debates he was already languishing in the polls. Next came Jeb Bush, the son and brother of two former presidents whose nomination was talked of as an inevitability, but his lacklustre campaigning skills soon became apparent as he became a human punching-bag for Mr Trump. Bush's withdrawal paved the way for the anointing of another Floridian as the establishment favourite, Marco Rubio, but by confusing youth and good looks for charisma and ability the party grossly overestimated Rubio's suitability. He dropped out of the race last night after coming a distant second in the Sunshine State, winning only his home county of Miami-Dade.
With Rubio gone, the once-colossal GOP field has been reduced to just three remaining candidates. This time last year, few would have expected Donald Trump to be one of the final three, let alone the overwhelming frontrunner, and just as unexpected as Trump's success has been the dogged survival of Ohio governor John Kasich, a man who only just made it onto the first debate stage back in August but has managed to keep his place at the top table throughout this campaign, outlasting better-funded and more media-savvy rivals.
It hasn't just been Kasich's electoral fortunes which have raised eyebrows; his public image has also been transformed over the course of this race as he has shedded his congressional reputation as a pugnacious veteran of the Gingrich era and adopted the mantle of affable Grandpa-In-Chief, dancing at rallies, hugging supporters and preaching an unashamedly moderate brand of compassionate conservatism. His skill has been to reach out to those voters who the GOP are so often accused of leaving behind - the working poor, the unskilled, the mentally ill and the drug-addicted - whilst refusing to bow down to the hard-right and instead passionately defending his record of expanding Medicaid in Ohio and calling for a more tolerant and loving approach towards LGBT issues.
Many mainstream conservatives, myself included, have long viewed Kasich with intense admiration whilst simultaneously dismissing his chances of winning the Republican nomination. Those chances have not risen over the course of the campaign, not even now as he enjoys the status of being the last remaining mainstream candidate, but with the possibility of a contested convention looking more and more likely, it is vital that Republicans unite around Kasich as the last hope for the party's sanity and electability.
It is equally important that mainstream conservatives reject the candidacies of Kasich's two Republican rivals, Mr Trump and Texas senator Ted Cruz. Despite its problems, the GOP remains a proud party with an even prouder history; it is the party of Abraham Lincoln and Teddy Roosevelt, of Dwight Eisenhower and Ronald Reagan, the party that ended slavery, expanded the franchise, introduced the first piece of civil rights legislation, ended the Cold War and stood up against global terrorism. America is strong when the Republican Party is strong, but if the GOP is to survive this current crisis it is vital that genuine conservatives decisively reject the uncompromising extremism of Senator Cruz just as vehemently as they reject Donald Trump's demagoguery. In such difficult times it is hard to see any light at the end of the tunnel, but by embracing either of these candidates the conservative movement risks losing its soul and thus rendering itself unfit for office.