The gloves are off in the escalating competition between President Donald Trump and Mike Bloomberg, with Trump taking shots at the former New York mayor’s physical stature and Bloomberg’s presidential campaign calling the president a “pathological liar.”

For weeks, tensions between the two New Yorkers have been simmering, as Bloomberg has risen in national polls of the Democratic primary race despite his late entrance and unconventional campaign.

Now those tensions are boiling over ahead of the Super Bowl on Sunday, with both Trump and Bloomberg airing ads during the game at a cost of more than $11 million.

Bloomberg’s campaign, responding to an interview in which Trump insulted the former mayor, suggested their strategy of getting under the president’s skin was bearing fruit.

Kevin Sheekey, Bloomberg’s campaign manager, told NBC News that "it is fair to say" that their "theory of the case is playing out, and we are on wartime footing."

The skirmish between Trump and Bloomberg comes as the former mayor prepares to kick off a whirlwind tour Monday of states not yet a top focus for his Democratic competitors: California, Michigan and Pennsylvania.

It’s a deliberate strategy to counter-program the Iowa caucuses on Monday, the formal starting gun for the primary contests and a critical test for most other Democratic candidates – except, perhaps, Bloomberg, who is skipping Iowa and the other early states.

While the rest of the Democrats anxiously watch the results come in from the first-in-the-nation Iowa caucuses on Monday, Bloomberg will be in Sacramento, Fresno and the Los Angeles area calling attention to California’s mail-in and early voting periods that start this week.

As Bloomberg and Trump prepared to air dueling ads during Sunday’s Super Bowl, both were already trading barbs. Trump dismissed the three-term mayor of his hometown as “very little” – a reference to his height.

"I just think of little. You know, now he wants a box for the debates to stand on. OK,” Trump told Fox News in a clip released hours ahead of his pre-Super Bowl interview with Sean Hannity. “It's OK. There's nothing wrong. You can be short. Why should he get a box to stand on? He wants a box for the debates. Why should he be entitled? Does that mean everyone else gets a box?"

He said New Jersey Sen. Cory Booker, who last month suspended his presidential campaign, "couldn't get all the things that Bloomberg's getting now," an apparent reference to the Democratic National Committee's decision to change the debate criteria in a way that allowed Bloomberg to qualify. Bloomberg, who is self-financing his campaign, no longer needs to attract a large number of individual donations, which had been a necessity to qualify for the earlier debates.

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

It was unclear what Trump was referencing in regards to Bloomberg requesting a box to stand on during an upcoming Democratic debate. Bloomberg, whose height was trending on Google Sunday, is listed as 5 feet, 8 inches tall.

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Bloomberg's campaign said there was no truth to Trump's remarks.

"The president is lying," Bloomberg campaign spokesperson Julie Wood said in a statement. "He is a pathological liar who lies about everything: his fake hair, his obesity, and his spray-on tan."

The former mayor echoed his spokesperson's remarks, saying that Trump "lies about everything so you shouldn't be surprised that he said things like that."

"I stand twice as tall as he does on the stage that matters," he added.

Bloomberg’s stops in California, Pennsylvania and Michigan this week illustrate how Bloomberg is sidestepping the early states in favor of delegate-rich states that hold their primary contests later in the year and general election battlegrounds that Democrats will need to defeat Trump in November.

In an illustration of Bloomberg’s no-holds-barred strategy, he planned to campaign in northern, central and southern California in the course of a single day Monday, taking a coterie of reporters along with him on a chartered aircraft.

The former mayor and billionaire businessman has hired hundreds of campaign operatives and field organizers in those and other states across the country – all paid for by funds he’s donating to his own campaign.

"Iowa and New Hampshire have 65 delegates. California, Michigan, and Pennsylvania have 726,” said Bloomberg campaign spokesman Galia Slayen.

But Bloomberg’s campaign has irked some of his Democratic rivals, who have spent months putting in facetime in Iowa and New Hampshire and meeting onerous criteria to make the debate stage.

That frustration has grown even as the focus in the Democratic primary turns to whether any of the other candidates will be able to stop Vermont Sen. Bernie Sanders, who many fear will be a less electable rival in the general election against Trump. Bloomberg has worked to portray himself as the middle-of-the-road candidate best positioned to defeat the incumbent GOP president.

As of Sunday, Bloomberg is in fourth place in the RealClearPolitics average of national Democratic primary polling.

Trump has spent the past few weeks attacking Bloomberg repeatedly on Twitter as Bloomberg ads blanket the airwaves.

Bloomberg’s 60-second spot airing during the Super Bowl focused on gun control, a key issue for the former mayor, and tells the story of a mother whose son – an aspiring football player – was killed by gun violence. Trump aired a 30-second ad about criminal justice reform that focused on Alice Marie Johnson, who had her life sentence in prison commuted by Trump.

Early Sunday morning, Trump tweeted that Bloomberg "is going nowhere, just wasting his money, but he is getting the DNC to rig the election against Crazy Bernie, something they wouldn’t do for @CoryBooker and others." They are doing it to Bernie again, 2016.

Calling Bloomberg "Mini Mike," Trump claimed Bloomberg was unfairly "negotiating" to "have the right to stand on boxes" during a future debate. He also said Bloomberg, whose business portfolio includes a major media outlet, said the candidate was "part of the Fake News."

After Bloomberg announced he was running for president, Bloomberg News said it would not investigate its owner and, as a result, any of the other Democratic candidates so to be fair. But it said it would still do so with Trump as the current occupant of the White House.

Responding to Trump's midnight posts, Bloomberg tweeted: "Looks like our ads are keeping you up at night."

"We've got one in particular you should watch today," he continued, pointing to the upcoming Super Bowl ad.

Bloomberg's campaign is bypassing the first four primary contests and instead focusing on gaining delegates in Super Tuesday states and those in the weeks to follow. He has built up a massive campaign staff and has pledged to keep spending through the general election even if he is not the Democratic nominee.

On ABC's "This Week," Democratic presidential candidate Andrew Yang said the new DNC debate rules might not be so appealing to Bloomberg, who has yet to participate in a debate as a result of the previous standards.

"So, I’m not sure that this is a development that he's going to welcome, frankly," Yang said. "I think the DNC looked at this and said, we need to get Bloomberg on the debate stage. This change is clearly tailor-made to deliver him to the debate stage."

He continued: "And the question is, whether this is a move that Mike's excited about it or whether Mike’s indifferent to or even negative towards.”