Sen. Luther Strange speaks to supporters after he conceded the Republican primary runoff for U.S. Senate to Roy Moore in Homewood, Ala. (Butch Dill/AP)

As he headed to Huntsville, Ala., in a last-ditch effort to lift the floundering campaign of Sen. Luther Strange, President Trump was fuming — feeling dragged along by GOP senators who had pleaded with him to go and increasingly unenthusiastic about Strange, whom he described to aides as loyal but "low energy."

His agitation only worsened on the flight back last Friday. Trump bemoaned the headlines he expected to see once Strange was defeated — that he had stumbled and lost his grip on "my people," as he calls his core voters. He also lamented the rally crowd's tepid response to the 6-foot-9 incumbent he liked to call "Big Luther."

"Trump was never fully behind Strange to begin with," former Republican National Committee chairman Michael Steele said Wednesday after Strange was trounced in Tuesday's GOP primary in Alabama. "But the party coaxed and cajoled him to get on the Strange train, and he did."

For Trump, the trip to Alabama marked the dispiriting start to one of the lowest and perhaps most damaging stretches of his already troubled presidency, leaving him further weakened and isolated with few ways out of the thicket of challenges he faces, according to a half-dozen people close to him interviewed on Wednesday.

His political vitality within his party — counted upon by Republicans who fear primary challenges in next year's midterm elections — suddenly stands in question, as neither his vocal campaigning nor millions of dollars from the Republican establishment could save Strange from defeat by insurgent challenger Roy Moore.

Trump's legislative agenda lies in tatters, as Senate Republicans failed again this week to rally around legislation that would gut former president Barack Obama's Affordable Care Act. He is also increasingly under siege by members of both parties for his administration's response to Hurricane Maria, which has left Puerto Rico devastated and begging for help from Washington.

By Wednesday, the downtrodden president tried to start anew by unveiling a tax plan at an event in Indiana — a proposal immediately met with withering attacks from the left as a deficit-busting giveaway to the rich and from the right as not aggressive enough in slashing tax rates. The Drudge Report, influential among conservatives, dubbed it "more betrayal."

Trump also waded back into the health-care debate, falsely stating that the Republican legislation was held up by a hospitalized senator.

"We have the votes for health care. We have one senator that's in the hospital. He can't vote because he's in the hospital," Trump told reporters on Wednesday — an apparent reference to Sen. Thad Cochran (R-Miss.), who turns 80 in December and has dealt with various health problems.

Cochran responded with a corrective tweet: "Thanks for the well-wishes. I'm not hospitalized, but am recuperating at home in Mississippi and look forward to returning to work soon."

Trump's loose, confident talk extended elsewhere on Wednesday. In Indiana, the president was full of bravado as he made his tax pitch — and if there was lingering frustration with Strange, he did not show it.

"These tax cuts are significant," Trump said at the state fairgrounds. "There's never been tax cuts like what we're talking about."

But Trump's critics did not buy the president's assurance and said the tax speech could not paper over his problems.

"In Alabama and with so many things, Trump has helped to light a fire he can't control, and there's no sign he knows how to get out of this situation," said Peter Wehner, a senior fellow at the Ethics and Public Policy Center who worked in George W. Bush's White House. "It's going to cause him to lash out more rather than less as he starts to feel like the walls are closing in."

Several of Trump's longtime friends and associates said he is doing what he always does in times of trouble: attempt to overwhelm with liveliness. But they acknowledged that Trump may not be enjoying the experience.

"I'm told he's unhappy," said veteran Republican consultant Roger Stone. "He's surrounded by people who don't understand politics and don't understand why he won the presidency. Instead of sending a message in Alabama to get behind his policies, they sadly lost the opportunity."

Said former Trump campaign aide Sam Nunberg, "The president will think about what happened in Alabama and remember everybody who told him to go all in. If you sent him polls from the [U.S.] Chamber of Commerce or the Senate Leadership Fund, the next polls you send will go in his trash can."

Together, those groups, along with other mainstream GOP organizations, spent more than $10 million to boost Strange.

Congressional Republicans, meanwhile, stewed over their own fates, anxious that Moore, a former state Supreme Court judge, would become a national burden for the party because of the long list of incendiary comments he has made on race, religion and sexuality.

Hushed talk of retirements dominated conversations on Capitol Hill, one day after Sen. Bob Corker (R-Tenn.) announced that he would not seek reelection in 2018, with Republican lawmakers wondering whether they could survive a GOP political storm that only seems to be growing.

Former White House chief strategist Stephen K. Bannon, who backed Moore and introduced him at his victory party, encouraged conservative outsiders in Mississippi and other states to move closer to launching Senate bids, one person close to him said.

"There's a big lesson here: Stick to the program," Bannon said Wednesday on Breitbart News's Sirius XM radio show. "There's a lesson, stick to the program, your base will be there, and you'll grow your base."

Steele, however, said Strange's defeat did not mean Trump had lost his political sway with Republican base voters.

"Voters in Alabama knew the whole endorsement for Strange was a wink and a nod. They got that Moore was a Trump guy," Steele said. "So did he endorse the candidate who lost? Yes. But the reality is more nuanced than 'Trump lost in Alabama.' He lost, but his voters know why and still love him."

In the West Wing, there was relative calm as officials plowed forward, hoping to leave behind the dramas of Alabama and Trump's campaign against NFL players protesting police brutality during the national anthem. They agreed with Steele that while the GOP was fractured, Trump's coalition remained.

"He knew what was coming in Alabama on Friday," said one person close to Trump. "He knew how McConnell had become an issue there — and he said as much over dinner on Monday." That evening, Trump had met with a group of prominent conservative leaders at the White House.

The person added, "What he wants to do is get back to taxes, make sure the Senate gets that done as soon as possible."

Aides said that Trump knew that those who privately supported his endorsement of Strange, such as White House chief of staff John F. Kelly, were doing so because Trump at first was eager to do so and saw a chance to patch up relationships in Congress.

Trump was defensive in his remarks about the race to reporters on Wednesday, a few hours after he deleted a series of pro-Strange tweets. He also characterized Senate Majority Leader Mitch McConnell (R-Ky.) as a drag on Strange.

"I have to say, Luther came a long way from the time I endorsed him, and he ran a good race, but Roy ran a really great race," Trump said, adding that Moore's campaign used McConnell as a weapon against Strange.

The atmosphere of uncertainty and recriminations following the Alabama race prompted Republicans, even those close to Trump, to feel urgency to pass something — anything — that could somehow stabilize the party.

"If there was ever a time when Republicans feel pressure to perform, it's now," said Rep. Mark Meadows (R-N.C.), the chairman of the House Freedom Caucus. "If big things don't get done by Thanksgiving, there really won't be enough spin to say Republicans here have done anything but fail."