COMPTON, Calif. (Reuters) - U.S. Democratic presidential contender Michael Bloomberg vowed on Monday he would not let President Donald Trump bully him and said the insults being lobbed at him are a sign Trump is worried about running against the fellow New York business tycoon.

“I think he thinks I’m going to beat him,” Bloomberg told Reuters in an interview in Compton, California, where he was campaigning. “And we’ve tried to get under his skin.”

A Reuters/Ipsos poll released on Thursday showed Bloomberg, a billionaire and former mayor of New York, moving into third place among registered voters for the 2020 Democratic nomination.

He trails front-runners Joe Biden and Bernie Sanders, who competed on Monday in Iowa’s caucuses, the traditional kickoff to the presidential nominating contest. Bloomberg is taking an unorthodox approach focused instead on larger, delegate-rich states such as California that start voting in March.

The party’s nominee will face Trump in the November election.

Trump told Fox News Channel’s Sean Hannity in an interview that aired on Sunday that Bloomberg, who stands about 5 feet 8 inches (1.73 m) tall, against the president’s 6 feet 3 inches (1.91 m), had requested a box to stand on during the Democratic debates.

The jab came after the Democratic National Committee scrapped a rule last week requiring that candidates meet a threshold of grassroots donations, opening the door for Bloomberg to participate in a Feb. 19 debate in Nevada.

Trump also has dismissed Bloomberg in a series of recent Twitter posts as “mini Mike.”

On Sunday, Bloomberg’s campaign denied it had requested a box and taunted the president’s “fake hair, his obesity and his spray-on tan.”

“I assume his staff says’ Don’t take the bait,’” Bloomberg said in the interview with Reuters. “He can’t control himself because he thinks I’m going to beat him.”

Earlier on Monday, Bloomberg told campaign events in California he would not let Trump bully him.

“Trump’s insults just don’t bother me,” Bloomberg said at a community college in Fresno. “I have never backed down from a bully or run away from a fight.”

With campaign stops across California on Monday, Bloomberg displayed his extremely well-funded campaign. Worth at least an estimated $60 billion, Bloomberg is the only candidate with deep enough pockets to essentially start a general election campaign, while his 10 Democratic rivals focus on the four early voting states of Iowa, New Hampshire, Nevada and South Carolina.

California is the largest of the 14 states to vote on March 3, a date known as Super Tuesday, when nearly a third of the 3,979 state delegates who select the Democratic nominee will be up for grabs.

As of Monday, Bloomberg had 220 full-time staffers in California, which will grow to 300 by the time the state votes, his campaign said. U.S. Senator Bernie Sanders, who is believed to have the second-largest presence, has about 80 staffers in the state.

Some California voters said they were just getting to know Bloomberg. “I came to see more about what his plans are,” said Jesse Gomez, 18, a student at the community college in Fresno.