CLEVELAND — Every convention embodies both the tug of nostalgia and the dream of coming political power. But never in memory has there been a political convention with so little use of the present tense.  

The politics of the past were on display Tuesday night when both Paul Ryan and Mitch McConnell delivered speeches that struggled to pretend that nothing had changed with the ascendency of Donald Trump.  

Ryan, the self-styled peddler of big ideas, claimed, “We, in this party, offer a better way for our country, based on fundamentals that go back to the founding generation.” McConnell, whose vision mostly consists of counting votes, bragged about how the 2014 elections sent “a freshman class of rock star Republicans to the Senate.”  

Both Ryan and McConnell are custodians of Republican memory.  

The House speaker, whose original political mentor was free-market visionary Jack Kemp, believes in the legacy of Ronald Reagan, the sainted Republican figure whose name he invoked in his convention speech. McConnell’s Senate career began when the “Gipper” was in the White House — and he originally came to Washington to serve in Jerry Ford’s Justice Department.  

The future is on display in Cleveland with every ambitious Republican who believes that the battle to win back the party begins the moment that Trump delivers his election night concession speech.  

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Ted Cruz is transparent with his 2020 ambitions. “You believe in tomorrow,” Cruz told his hardcore supporters at a Wednesday rally. And he feigned modesty when he declared, “I don’t know what the future will hold.”  

With John Kasich skulking on the fringes of the convention and up-and-coming GOP stars like Tom Cotton making pilgrimages to key early state delegations, it almost seems as if the 2020 Iowa caucuses will be held immediately after Labor Day.  

The lack of enthusiasm for the bilious billionaire at the top of the ticket is undeniable — no matter how loudly GOP mouthpieces claim that the party is coming together in support of its nominee. The largest group at this convention probably consists of the through-gritted-teeth Trump endorsers. They are the Republicans whose major ambition is to avoid being blamed if Trump goes down to defeat.  

Older GOP leaders may take comfort in memories of the steamy 1980s hit show “Dallas” about the rivalries and ruinous relationships in the family that controlled Ewing Oil. After the creaky plot reached a dead end, the scriptwriters boldly erased an entire season by portraying it as a bad dream.  

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That is what many Republicans are hoping — to wake up the day after the Cleveland convention to discover that the Trump nomination was an all-too-realistic nightmare. How comforting it would be for them to be transported to an orderly world in which someone like Marco Rubio or Ted Cruz — known political commodities — are running strongly against Hillary Clinton.  

Of course, it is not to be. The Republican leadership cannot get around the embarrassing reality that the GOP voters in the primaries opted for the authoritarian temptation in the form of Donald J. Trump. Nothing better symbolizes the Cult of the Leader than the parade of testimonials about the GOP nominee from the Trump family, who stand out at this convention for their sincerity.  

No matter how often GOP delegates talk about the menace of Hillary Clinton and the importance of appointing conservatives to the Supreme Court, it is impossible to portray Trump as a normal nominee of a political party that cares about the details of governing. By embracing Trump, the Republican leadership has put its integrity in a blind trust.  

Thursday night’s acceptance speech will be breathlessly billed as the most important moment of Trump’s career. But that will only be the case if the oft-married real-estate mogul plays against type. If somehow Trump shows humility or admits major mistakes, then maybe he can convince the gullible that a 70-year-old man can radically change with the help of a good speechwriter.  

But no matter how dramatic the final-night pyrotechnics and how artful the balloon drop, the speech will change little if it is just Trump again reciting familiar applause lines off a once-reviled TelePrompTer.  

And it is hard to realistically imagine any words that Trump could say that would convince the doubtful that he is prepared to govern at a time of anguish and worldwide instability. Not even Demosthenes or Cicero could pull off the rhetorical challenge that now faces this unlikely and outlandish GOP nominee.