WEST PALM BEACH, Fla. (Reuters) - U.S. President Donald Trump and Democratic presidential candidate Mike Bloomberg traded withering taunts on Sunday, in an exchange that suggests the Bloomberg campaign is willing to fight Trump’s notorious insults head on.

Trump’s remarks to FOX News Channel’s Sean Hannity, coupled with a series of Twitter posts late on Saturday, also indicate the president is keeping a wary eye on the billionaire and former New York City mayor as a potentially tough competitor who has the funds to outspend him.

A Reuters/Ipsos poll released on Thursday showed Bloomberg in third place among registered voters for the 2020 Democratic nomination after he spent millions of dollars of his own money on adverts.

Trump told Hannity in an interview which aired on Sunday that Bloomberg, who stands at about 5 feet 8 inches compared to the president’s 6 feet 3 inches, had requested a box to stand on during the Democratic debates.

Last week, the Democratic National Committee (DNC) scrapped a rule requiring that candidates meet a threshold of grassroots donations, opening the door for Bloomberg to participate in a Feb. 19 debate in Nevada. Bloomberg, a late entry to the race, has pledged not to take any donations and to finance his campaign by dipping into his estimated $60 billion fortune.

“He wants a box for the debates. Why should he be entitled to that? Really. Does that mean everyone else gets a box?” Trump asked Hannity during the interview which was taped on Saturday at the Republican president’s Mar-a-Lago club in Florida.

Trump, who often coins derisive nicknames for his political opponents, also unleashed a series of tweets dismissing Bloomberg as “mini Mike” on Saturday evening.

U.S. President Donald Trump waves as he boards Air Force One with First Lady Melania Trump at Joint Base Andrews in Maryland en route to West Palm Beach, Florida, U.S., January 31, 2020. REUTERS/Yuri Gripas

On Sunday, Bloomberg’s campaign denied it had requested a box and took aim at the president’s own personality and appearance.

“The president is lying. He is a pathological liar who lies about everything: his fake hair, his obesity, and his spray-on tan,” said Bloomberg spokeswoman Julie Wood.

During the interview, Trump also suggested the DNC was bending its rules to allow Bloomberg to participate in the debates.

“I think it’s very unfair for the Democrats. But I would love to run against Bloomberg. I would love it,” said Trump.

The battle of the billionaires began heating up last month when Bloomberg, who made his fortune as co-founder of the financial information and media giant Bloomberg Inc., debuted a television ad attacking Trump as “an erratic and out of control president.”

The two men are among the most wealthy to run for the White House, although Bloomberg’s personal fortune dwarfs Trump’s own wealth, which Forbes estimates at around $3 billion.

Some Trump advisers privately say they fear Bloomberg becoming the Democratic candidate because of his capacity to spend an estimated $1 billion or more to take on the president.

The Trump and Bloomberg campaigns were each spending $10 million to run adverts during the Super Bowl on Sunday night, which is watched by many millions of people.

Even if he does not win the Democratic nomination, Bloomberg has pledged to spend millions more on political ads before the November election.

“This is what happens when somebody like me rises in the polls,” Bloomberg told an audience at a campaign rally in Los Angeles later on Sunday when asked about Trump’s comments.

“All of a sudden the other candidates get scared and I think Donald Trump knows that I can beat him and that’s why he comes back with those kinds of comments.”