Over the past two years, there has been one constant in the increasingly chaotic world of U.S. politics: Donald Trump's tweets cause headaches for John McCain, Jeff Flake and other Senate Republicans.

The president's vicious and personal Twitter attack Thursday on MSNBC personalities Mika Brzezinski and Joe Scarborough set off a familiar round of outrage from Capitol Hill Republicans condemning the insults. According to a tally by the Washington Post, more than three dozen members of Congress from both parties denounced Trump.

One difference: Unlike 2016, when he was running for re-election in a volatile and unpredictable atmosphere, McCain was among the first to push back on Trump's tweet. While Arizona's senior senator and Trump have had a combative relationship, McCain last year flinched at having to routinely answer for Trump's assorted offensive and controversial comments, although at times he did so forcefully, such as after Trump belittled a Gold Star family.

"I'm just embarrassed. Embarrassed isn't the right word. I just regret it," McCain told NBC News in remarks played Thursday on MSNBC.

McCain also said that he was "not surprised but ... disappointed."

Another difference: Junior senator Flake, who prominently criticized Trump in 2016 and took some return fire from him on Twitter, is now the one running for re-election in 2018. Flake is facing a challenge in the Arizona Senate GOP primary from Kelli Ward, a former state senator from Lake Havasu City who is running as a Trump-style Republican, and he could face additional Trump-aligned foes.

As of Friday afternoon, Flake had not commented on Trump's rip on the "Morning Joe" co-hosts.

However, in response to The Arizona Republic's inquiry, Flake said in a single-sentence written statement: "This tweet, like many before it, is beneath the dignity of the presidency."

On Thursday, national Democrats signaled they intend to continue their 2016 strategy of tying offensive Trump tweets and remarks to Republicans on the ballot in 2018.

Sabrina Singh, deputy communications director for the Democratic National Committee, asked via Twitter if Flake had commented on Trump's Brzezinski tweets. "If not, his silence condones Trump's behavior," she tweeted.

From the moment he announced his presidential candidacy in June 2015, Trump was under continuous pressure and scrutiny for his angry and defiant style. He would routinely take to Twitter to blast his GOP primary opponents and others who criticized him.

In the latest episode, Trump ripped Brzezinski as "low I.Q. Crazy Mika" and dubbed Scarborough "Psycho Joe."

In a follow-up tweet, Trump claimed he met with Scarborough and Brzezinski in Florida around the first of the year and that "she was bleeding badly from a face-lift."

McCain, who has been on the receiving end of abrasive Trump tweets himself, brought up Trump's Brzezinski comments Thursday during his weekly Facebook Live town hall in which he answers selected questions from the public.

McCain suggested Trump's preoccupation with the TV show hosts is a distraction to issues such as foreign policy and national security.

"What is that all about?" McCain asked rhetorically.

"We have to pay attention to what the president does, not even what he says," he added.

During last year's Senate race, McCain withdrew his support of Trump as his party's presidential nominee after a 2005 recording surfaced of Trump making obscene and misogynistic comments about women.

But Democratic attempts to tether McCain, the 2008 GOP presidential nominee, to Trump were unsuccessful, and McCain handily defeated his opponent, then-U.S. Rep. Ann Kirkpatrick, to win a sixth Senate term.

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

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