Former vice president Joe Biden’s strong start since entering the crowded race for the Democratic presidential nomination has unnerved Donald Trump and his team, according to political observers.

Biden has surged to significant leads in many public opinion polls as front-runner in a pack of more than 20 candidates chasing the nomination to take on Trump next year. More than that, Biden defeats Trump in hypothetical match-ups, according to many of those same polls.

“They take him very seriously. Some of these advisers … they’re actually surprised at how much of a lead he’s opened up,” said Jonathan Swan, political reporter for the Axios news site. “They were always worried about Biden in a general election, but the consensus a few months ago is he can never — has no prayer of getting through this far-left Democratic primary. So there’s a little bit of uneasiness that, wow, maybe he could get through this Democratic primary.”

However, Trump is mistaken to antagonize Biden, according to former New Jersey governor Chris Christie who also ran unsuccessfully for the Republican presidential nomination in 2016.

Trump regularly taunts Biden as “Sleepy Joe.”

“I think it’s a mistake for him to be doing what he’s doing. Now, listen, there’s a lot of things that I thought he did mistakenly in 2016. He wound up winning and don’t remind me of that when we get off the air,” Christie said during a TV appearance. “But the point is that I think Joe Biden’s the one guy, and I’ve said this all along, who can go into Michigan and Wisconsin and Ohio and Pennsylvania and appeal to white working class voters.

“The president doesn’t need that type of opponent. He needs an opponent who will repel those white working class voters and keep his” base intact, Christie added.

Meanwhile, there is no evidence that connects Biden to any corruption due to Biden’s son’s involvement in a gas company in Ukraine, said Rep. Adam Schiff (D-Calif.).

Trump’s team, particularly Trump personal attorney Rudolph Giuliani, has been trying to ensnare Biden in Ukraine corruption in recent weeks as a political tool to take Biden down.

“I don’t know the circumstances in which [Hunter Biden] took the job but I can say this vis-à-vis Joe Biden, there’s no evidence nor has there ever been any evidence that he was doing anything but trying to get the Ukraine government to crack down on corruption,” Schiff said. “Now we’re providing generous support to Ukraine, we’re providing defensive weapons to Ukraine, we want Ukraine to be successful in its conflict with Russia. But part of that is happening in a government that the people of Ukraine are willing to fight for and protect.

“And they’ve had an endemic corruption problem. That’s what Joe Biden was trying to address. So going after his son is just a method of going after someone the president believes is his most formidable opponent,” Schiff added.

“So yes, let the president go after him, but don’t seek the help of a foreign government in your election,” Schiff said of a trip Giuliani intended to take on the matter to Ukraine but cancelled last minute. “And, you know, if this isn’t criminal and Bob Mueller said he could prove all the ailments of a crime, then maybe we need to change the ailments of that crime because we cannot make this the new norm that if you can’t win an election on your own, it’s fine to seek help from a foreign power.”