"Therefore, if the very dangerous & unfair Section 230 is not completely terminated as part of the National Defense Authorization Act (NDAA), I will be forced to unequivocally VETO the Bill when sent to the very beautiful Resolute desk," Trump added.

A senior House staffer said the issue has no chance of success with Democrats.

“It’s a fucking joke,” said the staffer, who spoke anonymously to discuss private negotiations. “This is a complex debate that has no business as an eleventh-hour airdrop.”

The senior staffer said the push to include other proposals targeting Section 230, even a bipartisan bill led by Senate Majority Whip John Thune (R-S.D.), in the defense bill won't make it either. “Full stop,” the staffer said.

The latest curveball from Trump comes as lawmakers rush to clinch a compromise defense bill this week. Democrats will almost certainly reject Trump's demand of a total repeal of the online protections.

The House and Senate passed their versions of the defense bill with enough bipartisan support to overcome a potential veto. It's unclear if those margins would hold up if Trump followed through on the threat.

It's the second time Trump has threatened to veto the defense bill. Over the summer, Trump pledged to tank the bill over a provision to remove the names of Confederate leaders from Army bases.

The base renaming issue was the greatest divide between lawmakers and the White House heading into negotiations, but lawmakers appeared to be inching toward a deal on the matter this week.

Axios reported Monday that the Trump administration had made a last-minute push to repeal Section 230, which protects online companies such as Facebook and Twitter from lawsuits over content posted on their platforms. Trump has sought to limit the protections, and even some Democrats have voiced concerns that the protections have been abused by social media companies.

An industry source who asked not to be named told POLITICO that Republican leaders on Capitol Hill have already told the White House that Democrats won't accept a full repeal as part of the defense bill H.R. 6395 (116).

Senate Republicans, instead, are aiming for more modest changes to the liability provision. Axios reported that Sen. Roger Wicker (R-Miss.), a member of the Armed Services Committee who also chairs the Commerce Committee that has jurisdiction over telecommunications issues, is pushing for negotiators to adopt his legislation to limit the protections in the final NDAA.

The defense policy bill is likely one of the last major pieces of legislation lawmakers will pass this year and before the end of Trump's presidency next month, making it a target for issues that aren't directly related to national security.

A repeal of online liability protections first emerged last month after White House Chief of Staff Mark Meadows floated a potential agreement in which Trump would drop his opposition to renaming military bases in exchange for repealing Section 230.

House Armed Services Chair Adam Smith (D-Wash.) said at the time that he would be open to compromise in order to finish the defense bill. And though he conceded social media platforms had abused their immunity, he downplayed the likelihood of Democrats agreeing to Trump's wholesale repeal of Section 230.

"I think these platforms are getting away with things they shouldn't get away with," Smith told the Council on Foreign Relations.

"The committees of jurisdiction will have something to say about this," he added. "And the president's motivation is transparent: he thinks social media was mean to him ... and he wants to sue them as a result, and he's looking for us to give him that power."

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