Donald Trump didn’t explicitly endorse a sitting Republican senator’s primary rival yesterday, but he came awfully close. The president, apropos of nothing, said via Twitter, “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. He’s toxic!”

Trump has already been at odds with Senate Republican leaders, and this won’t help, but what I found amusing were the White House aides who told Politico how surprised they were.

Trump aides were taken aback by the tweet. Many of them are deeply skeptical about Ward’s ability to defeat Flake. In 2016, Ward received 39 percent of the vote in an unsuccessful effort to unseat GOP Sen. John McCain. More recently, she came under fire for saying that McCain should step down from the Senate “as quickly as possible” after he was diagnosed with brain cancer. […] It is not the first time that Trump has caught his team off guard on political matters. Last week, the president announced on Twitter that he was endorsing Alabama Sen. Luther Strange in an upcoming special election, a move that directly contradicted the advice of aides who urged him to stay out of the fight, which has pitted establishment Republicans against the conservative base.

As an electoral matter, the White House aides appear to have given Trump good advice: Ward is almost certainly a weaker statewide candidate than Flake, which makes the president’s praise strategically unwise, and the president probably would’ve been better off staying out of Alabama’s Senate primary.

But the entertaining part of this is the ongoing White-House-aides-were-taken-aback series, which appears to have an endless number of episodes.

Trump’s aides were surprised to learn, for example, that he’d announced via Twitter that Christopher Wray was his choice to lead the FBI. They were equally startled to read Trump’s tweets banning transgender Americans from military service.

As we discussed a couple of weeks ago, White House aides also didn’t know in advance that Trump would falsely accuse Barack Obama via Twitter of tapping his phone. They also had no idea that the president would tweet news about his new chief of staff. Politico recently highlighted an instance from earlier this year in which Trump lashed out at China via Twitter “while U.S. officials were meeting with a Chinese delegation at the State Department.”

My personal favorite was this recent Associated Press report:

Aides to President Donald Trump were in deep talks about how to defuse tensions between Qatar and other Arab nations when the door to the secure room at the White House burst open. The urgent message: Trump had just tweeted about Qatar. One adviser read the tweet aloud and with that, the policymakers in midconference call had no other choice but to rework their plans to reflect the president’s tweeted assertion that Qatar, host to some 11,000 U.S. troops, was funding terrorism. It was an accusation against a close U.S. ally that had never been voiced so publicly and with such indelicacy.

It’s easy to feel some sympathy for the U.S. officials who find themselves blindsided by an erratic president who’s capable of waking up on any given day and declaring just about anything that pops into his mind. It’s a dangerous dynamic that makes it exceedingly difficult for a variety of dedicated professionals to do their jobs.

But at a certain point, everyone has to start expecting the unexpected. White House officials may successfully convince Trump to pursue a specific course of action, but given what we’ve seen so far this year, they should remain prepared to see the president do the exact opposite soon after – without warning or explanation.

Stop expecting consistent and rational behavior from Trump and you won’t be “taken aback.”