As a parent of a 4-year-old, I am now more keenly aware than ever of the flexibility of language. If you haven’t been asked to explain, for example, what we mean by “cool” in the context of slang, I encourage you to think about the intricacy of the task.

Or, more topical to the moment, consider the word “killer.”

This was long one of Donald Trump’s preferred descriptors for people he considered tough. The negotiators from other countries who were dealing with the United States, he insisted during the 2016 campaign, were “total killers,” as were the negotiators he’d pull from Wall Street to face off with them. His business troubles in Atlantic City? You need to understand that the lenders “weren’t babies” but were, instead, “total killers.” Some Democrats or members of the media were also killers, which Trump offered as a warning. Being identified as a killer in the context of finance, dealmaking or politics constituted a compliment from the former president.

He also used the term in its more literal formulation, of course. MS-13 gang members were killers, as were some nebulously bounded group of immigrants. To Trump, the effect was the same: that frisson of danger which he used either as praise or condemnation.

Then there were the edge cases, those whose strength Trump admired but who were, you know, killers. Like Russian President Vladimir Putin.

Over and over, Trump was presented with questions about the frequency with which critics of Putin met with untimely ends. And over and over, Trump demurred, either shrugging at others’ concerns or equating Putin’s behavior with that of the United States.

In December 2015, Trump appeared on MSNBC's “Morning Joe,” where the hosts challenged him on his appreciation of a compliment he claimed Putin had given him. (Putin hadn't, really, but that's a different story.)

“He kills journalists that don't agree with him,” Joe Scarborough said to Trump.

“Well, I think that our country does plenty of killing, too, Joe,” Trump replied.

A few days later, Trump tried to contextualize his response.

“Nobody has proven that he's killed anyone,” he said on ABC's “This Week.” He offered an odd addendum: “You're supposed to be innocent until proven guilty, at least in our country. It has not been proven that he's killed reporters.”

After being elected president, Trump was interviewed by Fox News. Bill O'Reilly again challenged Trump on Putin, calling the Russian president a killer.

“There are a lot of killers,” Trump replied. “Do you think our country is so innocent?”

Over and over, Trump declined to apply the term to Putin directly, excusing or downplaying what Putin’s alleged to have done. (It is true that Putin has not been tried for and convicted of murder, but setting that as the bar for culpability seems a bit naive.) It was a subtle part of Trump’s long-standing antipathy toward holding Putin to account, an approach that helped contribute to questions about his relationship with the Russian leader.

Trump responded to those questions with dubious assertions about how he’d been tougher on Putin and Russia than any other president. After news reports last year suggested that Russia was again hoping to influence the presidential contest to defeat Trump’s opponent, Joe Biden, Trump rejected the idea.

“If I win — they’re hoping that Biden gets in, because — and China is hoping that Biden gets in,” he said in an interview on Fox News in September. “Russia, probably they want Biden, because look, nobody’s been tougher to Russian than me, nobody.”

In August, he'd made a similar claim: Russia, China and Turkey were all hoping for Biden's election because of how tough Trump himself had been.

Intelligence officials disagreed. This week, the director of National Intelligence released a report outlining how Russia and Iran, in particular, had sought to influence the outcome of the 2020 election, with Russia’s preferred candidate being Trump, not Biden. Putin himself had likely been involved in pushing for Trump’s success, the report suggested, in keeping with the Russian effort in 2016.

Why? Because “Russian leaders viewed President Biden's potential election as disadvantageous to Russian interests,” the report states, even though the country did view some Trump policies as “anti-Russia.”

Earlier this week, President Biden offered a symbolic glimpse of the difference between his approach to Russia and Trump's.

“So you know Vladimir Putin,” ABC News's George Stephanopoulos said to Biden in an interview. “You think he's a killer?”

“Mmm hmm,” Biden replied. “I do.”

That one passive declaration, a seemingly obvious one from an American president, triggered a robust response from Russia.

“These statements from the president of the United States are very bad,” Putin's spokesman Dmitry Peskov said in response. (If Peskov's name sounds familiar, it may be because he was involved in an effort by Trump's attorney to negotiate a real estate deal in Moscow in early 2016.) “It is clear that he does not want to get the relationship with our country back on track, and we will proceed from that,” Peskov added.

A senior member of Russia's parliament called the remarks “boorish.” Putin himself offered a rubber-glue rejoinder: “It takes one to know one.” Russia recalled its ambassador to the United States, either because of Biden's comment, because of that report on Russian interference or both.

Geopolitics is a complicated thing, and Russia's response may be exaggerated for effect. But there was a response, one that reflected frustration with Biden — something which Trump's what-even-is-a-killer commentary never yielded. All for an “I do.”

Putin's response wasn't simply to imply that Biden was somehow a killer. He also offered a comment which, given the context, has a necessarily sinister edge.

“I would say to him: I wish you good health,” Putin said.

Language is an intricate thing.