WASHINGTON — Senate majority leader Mitch McConnell is wrestling with an unenviable, arguably impossible task this election year: protecting Senate Republicans from the political upheaval caused by Donald Trump’s presidential candidacy.

If he fails it won’t be for lack of preparation, hard work, and cold-blooded calculation.

In many ways Trump’s polar opposite, the close-mouthed, deliberate, uncharismatic McConnell maneuvered into his dream job as majority leader just last year, and has been working every angle to ensure he hangs onto it even if a backlash against Trump provokes a Democratic tidal wave. If they keep the presidency, Democrats need to pick up four Senate seats to take back the majority.

For McConnell, 74, avoiding that outcome means running a Senate schedule designed to assist a handful of vulnerable GOP incumbents in states such as Pennsylvania, New Hampshire, and Ohio. He’s allowing them to take votes and stack up accomplishments on issues like opioid addiction that they can brag about to voters back home. ‘‘It’s certainly helped me,’’ said one of those lawmakers, Senator Ron Johnson of Wisconsin.

It means having the foresight to push for an independent super PAC run by allies that is focused solely on Senate Republicans, built on a model that helped McConnell himself to a resounding reelection win in Kentucky two years ago. The Senate Leadership Fund, run by his former chief of staff Steven Law, announced this week it was reserving nearly $40 million in air time for the fall in five states.

And it means a delicate dance with Trump, whom he was quick to endorse in May, declaring that Trump had ‘‘won the old-fashioned way — he got more votes than anybody else.’’ The approach was markedly different from that of House Speaker Paul Ryan, whose hesitation before finally backing Trump provoked weeks of headlines on GOP infighting, and private grumbling from some Republicans who thought Ryan should have acted more like McConnell.

Since then McConnell has picked his moments on Trump. For two weeks running at his weekly Senate press conferences he refused to engage on questions about the ‘‘the presidential candidate,’’ as he referred to Trump. This week, nobody asked. But in a series of interviews to promote his new memoir, ‘‘The Long Game,’’ McConnell has mostly answered directly and offered frank criticisms, declaring that Trump can’t win without improving his measly fund-raising numbers, needs to stop criticizing people, start reading off a script, and in short behave like a ‘‘serious candidate.’’

The two men have spoken privately on a number of occasions, and McConnell himself notes that Trump has started to become more scripted, whether or not that is a result of taking his advice. Allies say his handling of Trump is typical of the taciturn McConnell, who is preternaturally disciplined and focused on what he can control, tuning out what he cannot.

‘‘I think he’s been a model for how you handle the Trump phenomenon in a way that generates the least amount of daily news,’’ said Law, his former chief of staff. ‘‘Others, either by equivocating or by alternatively feeling like they needed to respond to every news cycle, have generated more headaches for themselves than necessary.’’

In his new book McConnell recounts overcoming childhood polio with his mother’s help, being ordered by his father to beat up the neighborhood bully, and locking down endorsements from the popular kids to become president of his high school class. Slightly bug-eyed with multiple chins, McConnell has a demeanor that can at times be so staid as to seem comical. His staff is extremely devoted, generally a marker of a lawmaker’s character.

McConnell was personally involved in getting former GOP presidential candidate Marco Rubio to agree to run for reelection to his Senate seat in Florida, urging fellow senators to lean on Rubio, who had pledged repeatedly to retire. Rubio changed his mind, a decision Republicans believe will all but ensure they hang on to his Florida seat. McConnell allies also got involved in the May GOP primary in Indiana to ensure a winner, Representative Todd Young, heavily favored to prevail in the general election.

Allies give McConnell credit for Republicans’ success this year in avoiding self-destructive primaries that resulted in fatally weak candidates for Senate, something that happened repeatedly in 2010 and 2012.

This year, Republicans face a daunting Senate map that has them defending 24 seats, including highly vulnerable incumbents around the country.

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