WASHINGTON (AP) — President Donald Trump had just headlined a rally in Louisville, Kentucky, where Majority Leader Mitch McConnell was booed by home-state voters far more enamored with the president than with their longtime GOP senator.

WASHINGTON (AP) — President Donald Trump had just headlined a rally in Louisville, Kentucky, where Majority Leader Mitch McConnell was booed by home-state voters far more enamored with the president than with their longtime GOP senator.

Now the two were flying back to Washington aboard Air Force One, and as Trump dined on lasagna, he and McConnell talked throughout the hour-and-40-minute flight, according to Rep. James Comer, R-Ky., who witnessed the encounter.

It was a meeting of opposites: Trump brash, impulsive, boastful, and undisciplined; McConnell reserved, deliberate, methodical, and focused.

But despite their differences, Comer later recounted, what he saw on board that night were two men who knew they needed each other, and had something important in common: the desire for wins on shared goals.

"I felt like there was a mutual respect between the two men," Comer said. "McConnell knows how popular Trump is in Kentucky. And I think McConnell knows that there are areas that he can help the president on — and there are areas the president can help McConnell."

That flight in March helped cement a relationship that's now at the center of the Washington crucible. As controversy swirls over Trump's abrupt firing of FBI Director James Comey, McConnell's moves will set the tone for how the rest of the Senate and Republican Party as a whole responds. And if Trump is able to move past the mounting scandal and get his health care legislation and other priorities back on track, he may have the taciturn Kentuckian to thank.

For now McConnell is sticking with Trump, brushing aside Democratic calls for a special prosecutor to investigate Russia's ties to the Trump campaign, and ridiculing Democrats as hypocrites for bemoaning the Comey firing despite criticizing the former director themselves.

Yet at the same time, McConnell has not revealed his own views on Trump's conduct, in keeping with his approach to Trump from the moment the mogul secured the GOP presidential nomination. Unlike House Speaker Paul Ryan, R-Wis., McConnell did not hesitate, immediately endorsing Trump and sticking with him without wavering.

He's largely limited his comments to saying Trump should stop tweeting.

"I have plenty of questions to answer about things we're actually doing, like trying to repeal and replace Obamacare," McConnell, 75, told The Associated Press in an interview the morning after his trip with Trump on Air Force One. "I have my hands full without engaging in kind of daily commentary on the president's comments."

U.S. House Speaker Paul Ryan (R-WI) (L) and Senate Majority Leader Mitch McConnell (R-KY) speak to reporters after meeting with President Trump at the White House. Thomson Reuters

As for Trump, associates of both men say McConnell earned his esteem by his handling of the Supreme Court vacancy, which the Senate filled last month by confirming Neil Gorsuch. Despite angry Democratic protests, McConnell kept the vacancy open throughout the last year of Barack Obama's term, and then shepherded Gorsuch through almost seamlessly, even though it required breaking Senate rules to do it. Gorsuch's confirmation stands as the biggest victory thus far of Trump's presidency.

That demonstrated to Trump McConnell's mastery of the Senate, in stark contrast to Ryan's shaky leadership on health care legislation in the House, which collapsed in March before finally passing last week.

"Unlike Speaker Ryan who's relatively new to his job and also relatively new to leadership, McConnell's been doing this a long time and that's an asset you want to utilize," said Trey Grayson, head of the Northern Kentucky Chamber of Commerce.

Grayson said it will be up to McConnell to try to moderate Trump's expectations about the Senate's approach on health care given the impatience he's already demonstrated with Congress' slow-moving ways.

The White House has indicated it plans to take a more hands-off approach in the Senate than it did in the House on health care, and leave the job largely up to McConnell. For his part, despite establishing a working relationship with Trump, McConnell has not made a habit of engaging in the frequent or even daily phone chats that Ryan boasted of with the president, at times preferring to work instead through Vice President Mike Pence, a more predictable and known quantity.

Trump has caused the occasional problem for McConnell even apart from the repeated controversies of his administration. Ignoring pleas from GOP leadership, Trump appointed Montana GOP Rep. Ryan Zinke as Interior secretary, taking him out of contention as a Senate candidate in Montana. But more recently Trump has appeared to try to ingratiate himself with McConnell, choosing a McConnell favorite, Amul Thapar, as his first circuit court nominee.

Mitch McConnell. Win McNamee/Getty Images

The Trump-McConnell relationship dates to when the Senate GOP leader fended off a primary challenge from tea party candidate Matt Bevin, now Kentucky's governor, in 2014.

The future president met briefly with McConnell at the annual Conservative Political Action Committee in 2013, and invited McConnell to visit him at Trump Tower. Trump subsequently wrote a $50,000 check, Trump's largest individual donation that year, to McConnell's super PAC, which was followed by other substantial donations.

Now the fate of Trump's legislative agenda, and perhaps even his presidency, rests with McConnell, who in his sixth term has survived presidents of both parties. There's never been one as unpredictable as Trump, but don't expect that to change McConnell.

"All the presidents he's dealt with bring different personalities to the job but I think the constant is McConnell," said Scott Jennings, an ally and GOP strategist in Kentucky. "McConnell, he never changes."

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Associated Press writers Ken Thomas in Washington and Adam Beam in Frankfort, Ky., contributed.