Donald Trump is trying out a new moniker for Hillary Clinton

Republican presidential frontrunner Donald Trump appears to be test-driving a new moniker for Hillary Clinton, his Democratic counterpart. 

At a Saturday rally and in a tweet Sunday, Trump referred to the former secretary of state as "crooked Hillary."

"I'm not controlled by these special interests, by the lobbyists. They control crooked Hillary. And they control lyin' Ted Cruz," Trump said at a Saturday rally in Watertown, New York.

"Crooked Hillary Clinton is spending a fortune on ads against me," he added in a Sunday tweet. "I am the one person she doesn't want to run against. Will be such fun!"

Trump has made pet names a signature part of his brash campaign style. He referred to former Florida Gov. Jeb Bush, for example, as "low energy," and Sen. Marco Rubio as "little Marco." His moniker for Cruz, meanwhile, has become a regular chant for supporters at his rallies recently.

Clinton, for her part, responded Sunday by saying she couldn't "care less" about Trump calling her by the nickname.

"I don't respond to Donald Trump and his string of insults about me. I can take care of myself," she said on ABC's "This Week."

She said she was "concerned," however, about his attacks on women, Muslims, and immigrants, among others.

"He is hurting our unity at home," she said. "He can say whatever he wants about me. I really could care less. I'm going to stay focused on the issues."