Instances Donald Trump ominously warned someone to 'be careful'

Huge. Winning. Classy.

When Donald Trump finds a word or phrase he likes, he sticks with it. To wit: The 100-plus times Trump assured us that America is a laughingstock. Or the many times he has called someone a "friend of mine."

Over the weekend, he resurfaced another time-tested Trumpism: The often vague warning to us, to you, to them - to someone - to "be careful."

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This time, he aimed those words at Democratic presidential candidate Bernie Sanders, who Trump accused of sending protesters to disrupt his rallies. It was at least the fourth time this month that he used some version of the phrase.

Below, we carefully rounded up instances of Trump urging such caution to everyone from the Wall Street Journal editorial board to President Obama.

Trump tweeted, Bernie Sanders is lying when he says his disruptors aren't told to go to my events. Be careful Bernie, or my supporters will go to yours!

"We have to be very vigilant. We have to be very careful. And we can't allow people coming into this country who have this hatred of the United States." - March 10, to CNN's Anderson Cooper

"The Republicans are eating their own. They've got to be very careful." - March 5, at a Kansas rally

"He has to be very careful." - March 3, to CBS News's Major Garrett, about Sen. John McCain, R-Ariz.

Trump tweeted, Make sure you get on the Trump line and are not mislead by the Cruz people. They are bad! BE CAREFUL.

Trump tweeted, I hear the Rickets family, who own the Chicago Cubs, are secretly spending $'s against me. They better be careful, they have a lot to hide!

He tweeted, Hillary, when you complain about "a penchant for sexism," who are you referring to. I have great respect for women. BE CAREFUL!

Trump tweeted, The Hillary Clinton staged event yesterday was pathetic. Be careful Hillary as you play the war on women or women being degraded card.

John Harwood tweeted, Trump after being told Christie now says NJ Muslim celebrations didn't happen: "He really needs to be careful about what he says"

Trump tweeted, The @WSJ Wall Street Journal loves to write badly about me. They better be careful or I will unleash big time on them. Look forward to it!

"Carly was a little nasty to me. Be careful, Carly. Be careful." - Aug. 14, at a New Hampshire rally

Trump tweeted, The failing @HuffingtonPost and dopey @ariannahuff are writing so much false junk about me-they just can't get enough! BE CAREFUL.

Trump tweeted, Republicans must be careful with immigration-don't give our country away.

He tweeted, @BarackObama should be careful questioning @MittRomney on diplomacy--how many times has Obama apologized for our country on foreign soil?!

Trump tweeted, Paul Ryan's budget is very dangerous for the Republicans--just before the election--be careful!