Hillary Clinton may or may not be the all-around worst presidential nominee in the history of the Democratic party. That party has, over the years, thrown up some pretty unappealing characters. It’s also nominated candidates whose policies did (James Buchanan, Jimmy Carter) or would have done (George McClellan, George McGovern) great harm to the nation.

The Republican party has, on the whole, had higher standards or at least better luck. Since its first convention in 1856, it has nominated 27 men to serve as president of the United States. Not all have been of sterling quality. Even the most loyal Republican will acknowledge that there have been times when perhaps GOP nominees fell short of the standard for the presidency set forth in Federalist 68, that "it will not be too strong to say, that there will be a constant probability of seeing the station filled by characters pre-eminent for ability and virtue." It would not perhaps even shock a loyal Republican to say that over the long history of the GOP there have been times when it was perhaps as well that the Republican nominee did not prevail in the general election.

But we do think it fair to say, tipping our hat to recent revisionist studies of Warren G. Harding, and making allowances for a few unfortunate stumbles by Richard M. Nixon, that none of the previous GOP nominees was an embarrassment or a disgrace. I can say, as someone who has cast votes for the Republican presidential nominee in the eleven elections of my adult lifetime, that in no case have I felt it necessary to engage in serious second thoughts about the propriety of my choice.

But now the presumptive nominee of the Republican party, heir to the distinguished mantle of Abraham Lincoln and Ronald Reagan, of Ulysses S. Grant and Dwight D. Eisenhower, and, yes, of Tom Dewey and Gerald Ford and John McCain and Mitt Romney, is one Donald J. Trump. If Trump is nominated on Thursday, it will not be a grand day for a grand old party. For it will have nominated the worst nominee in its history.

There were many moments over the past year when this fate could have been avoided. The weakness not to say debility of several elements of the Republican party is an important topic for another day. For now, the last chance to save the Grand Old Party from itself rests with the delegates to the 41st Republican Convention. If they succeed, all honor to them. If they fall short, their failure will merely mark the final act of the Lamentable & Extraordinary Republican Tragedie of 2016.

At this melancholy moment for Republicans and conservatives, the conclusion of Winston Churchill's great speech in the House of Commons of March 24, 1938, comes to mind. Not because we think Donald Trump's nomination is in any way comparable to the Anschluss. And not because we think this era is comparable to the eve of World War II. But because we do think, for all of its farcical aspects, it is a moment of some gravity.

Here's Churchill:

For five years I have talked to the House on these matters, not with very great success. I have watched this famous island descending incontinently, fecklessly the stairway which leads to a dark gulf. It is a fine broad stairway at the beginning, but after a bit the carpet ends. A little further on there are only flagstones, and a little further on still these break beneath your feet.

For our part, we have watched the party descend a stairway. Now the carpet has ended. The flagstones are broken beneath our feet. A dark gulf awaits.

Perhaps the party, and the principles for which it stands, can emerge from this episode without lasting damage. After all, a distinguished party's traditions are not undone in a day or a year. They will remain available to us as a source of education and encouragement. Donald J. Trump may become the 2016 Republican nominee. He cannot be allowed to define the future of a great party that can, we trust, be made great again.