President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Tuesday used a taxpayer-funded trip to mock his potential 2020 Democratic rivals.

Speaking at a liquified natural gas facility near Lake Charles, La., Trump singled out former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE, Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), former Rep. Beto O’Rourke (D-Texas), South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegThe Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice Hillicon Valley: FBI, DHS warn that foreign hackers will likely spread disinformation around election results | Social media platforms put muscle into National Voter Registration Day | Trump to meet with Republican state officials on tech liability shield MORE and Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.).

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“Boy, you got some beauties there. Three hundred fifty million people and that’s the best we can do. I don’t think so,” he quipped.

Past presidents generally refrained from injecting partisan politics into official White House events paid for with public funds, but Trump has frequently broken that norm during his time in office.

The president joked about the dynamic last August when he noted how many reporters traveled with him to Charlotte, N.C., for a bill signing during the lead-up to the midterm elections, saying “it's like a political event and you don't even have to pay for it.”

Taxpayers also foot the bill for the president’s political travel, but the costs are typically reimbursed by his campaign or related PAC. Trump is attending a pair of fundraisers later on Tuesday in nearby Metairie, La.

Trump was touting his record on jobs and the economy during his official speech, when he launched into the attacks against Democrats vying for their party’s 2020 presidential nomination, saying, “You dream about competition like that.”

He sounded out Buttigieg’s name as “Boot-edge-edge” and took note of O’Rourke’s dive in the polls by recalling the former congressman’s assertion to Vanity Fair that he was “born to be in it.”

“Beto’s falling fast. What the hell happened? Remember about four weeks ago he said, ‘I was made for for this.’ He was made for it. He was made to fall like a rock,” Trump said.

The president also dismissed O’Rourke’s attempt to “reboot” his campaign, saying “that generally doesn’t work out too well.”

Trump also repeated his belief that Sanders has an edge on Biden, even though most polls show the former vice president is the clear front-runner in the Democratic primary field.

“I don’t know what the hell happened to Biden. What happened to him? I’m looking, I said, ‘That doesn’t look like the guy I knew,’” Trump said, before adding, “Bernie’s crazy. But Bernie’s got a lot more energy than Biden, so you never know.”

He then took a swipe at the self-professed democratic socialist, saying, “Bernie’s got a lot of energy but it’s energy to get rid of your jobs.”

The president predicted his Democratic opponent in 2020 would be “one of these people” and not Warren, whom he referred to by the derisive nickname “Pocahontas.” Trump said the Massachusetts senator “is probably out.”