By President Donald Trump standards, U.S. Sen. Jeff Flake got off pretty easy.

Despite anticipation that the president was set to rhetorically throttle Flake, R-Ariz., at his Tuesday night rally in downtown Phoenix, Trump only took a couple of swings at Flake and didn't even call him out by name.

The president did not, in fact, utter the names of either Flake or U.S. Sen. John McCain, another Arizona Republican Trump antagonist. It was an apparent nod to White House advisers who want Trump to appear and act "presidential."

But even without his mentioning names, the conservative audience knew who Trump was criticizing and roared their support of the president.

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After criticizing McCain for his July 28 vote torpedoing the GOP "skinny repeal" health-care bill, Trump turned to Flake: "Nobody wants me to talk about your other senator, who's weak on borders, weak on crime."

"Nobody wants me to talk about him. Nobody knows who the hell he is," Trump jeered. “See, I haven’t mentioned any names. So now everybody’s happy."

Trump has held a grudge against Flake since last year, when he was one of Trump's highest-profile GOP critics during last year's presidential race. Flake refused to endorse or even vote for his party's nominee.

He also has been a critic of several of Trump's signature policy ideas, including plans for a wall on the U.S.-Mexico border that the U.S. would force Mexico to finance.

"Senator Flake has a strong record on border security," Flake campaign spokesman Will Allison said after the rally. "He remains focused on working for Arizona and building a winning campaign."

On Wednesday morning, Trump took another swipe at Flake via Twitter, but his tweet, too, seemed somewhat restrained by Trump standards.

"Phoenix crowd last night was amazing - a packed house," Trump wrote in the message. "I love the Great State of Arizona. Not a fan of Jeff Flake, weak on crime & border!"

Any chance that Trump might overlook Flake's re-election bid probably vanished with the Aug. 1 publication of the senator's new book, "Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle."

In the book, which has been on the New York Times best-sellers list for two weeks, Flake takes the Republican Party to task for abandoning traditional conservative principles such as free trade, for Trump-style populism, nationalism and protectionism. It also speaks of the need to return to a civilized political dialogue.

The book generated national publicity for Flake as a Republican senator standing up to Trump.

RELATED: 7 things in Flake's book that could haunt his re-election campaign

Trump shot back Thursday with a Twitter message in which he seemed to endorse Kelli Ward, the former state senator from Lake Havasu City who launched a 2018 primary bid against Flake not long after losing her 2016 bid against McCain.

"Great to see that Dr. Kelli Ward is running against Flake Jeff Flake, who is WEAK on borders, crime and a non-factor in Senate," Trump tweeted. "He's toxic!"

President Trump appears to endorse Kelli Ward in tweet bashing Sen. Jeff Flake

Ward gets boost

While not an explicit endorsement, Trump's tweet gave a boost to Ward over other possible entrants in the race.

A poll released Tuesday by the Phoenix Republican consulting firm HighGround Public Affairs showed Ward leading Flake 42.5 percent to 28.2 percent in the 2018 GOP primary race. Another 24.2 percent either didn't know or refused to answer, while 5.1 percent preferred some other candidate.

The live telephone survey of 273 "high efficacy" Republicans or GOP-leaning independents has a margin of error of plus or minus 5.93 percentage points. It was conducted Friday and Saturday, after Trump's pro-Ward tweet.

In more bad news for Flake, the same poll also showed him trailing by 8 percentage points to U.S. Rep. Kyrsten Sinema, D-Ariz. — who is considering entering the Senate race on the Democratic side — 40.5 percent to 32.5 percent, with the rest undecided or refusing to answer.

The margin of error for the full sample of 400 voters has a margin of error of plus or minus 4.88 percentage points.

RELATED: Is Rep. Kyrsten Sinema running for Senate? Signs point to yes

In a Tuesday afternoon interview, Flake was nonchalant about Trump and his electoral prospects.

"That's why you run campaigns," Flake told The Arizona Republic. "We've always said we'll have a tough campaign both in the primary and the general. I have a race to run and I have a day job, obviously, and that's most important."

Ward was on hand at the Trump rally, and her campaign supporters were busy working the crowd despite 100-plus degree temperatures.

However, Ward had no formal role in the event, and while many of her supporters waved Ward campaign placards while waiting in line to get into the convention center, they weren't allowed to bring them inside. Trump did not mention her from the stage.

Flake gets backing

The Trump vs. Flake feud could have more implications than the typical Trump grudge match. Senate Majority Leader Mitch McConnell, R-Ky., and other Republican leaders and the National Republican Senatorial Committee, the arm of the national GOP that works to elect Republicans to the Senate, have made it clear they are backing Flake's re-election. Republicans control the 100-member Senate with a 52-member majority.

On Tuesday, the Senate Leadership Fund, a pro-McConnell Super PAC, launched a digital ad taking aim at Ward. It uses one of the same lines of attack on Ward that McCain used in 2016, attempting to tie her to the fringe "chemtrails" conspiracy theory.

Anti-government conspiracy theorists believe that the visible contrails of airplanes are really dangerous chemicals that are part of a plan to either control the weather or something more malevolent.

As a state senator, Ward organized a "chemtrails" forum in Kingman in 2014. She has maintained that she was merely responding to community concerns and never actually believed in "chemtrails" herself.

TALKING POLITICS: Listen to our Arizona politics podcast, The Gaggle, on Apple Podcasts, SoundCloud, Stitcher or Google Play.

Arizona state Treasurer Jeff DeWit, who is close to Trump, has been talked about as a possible Senate candidate for months, but such speculation has cooled. DeWit acted as emcee for Trump's rally in Phoenix.

Robert Graham, a former Arizona Republican Party chairman, has been mentioned as a possible candidate. His daughter led the crowd in the Pledge of Allegiance.

Political unknown Nicholas Tutora, a pro-Trump pharmacist from Phoenix, recently entered the GOP Senate race. He also was in attendance at the Trump rally.

Dan Nowicki is The Arizona Republic's national political reporter. Follow him on Twitter @dannowicki.

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