Sen. Lindsey Graham (R-S.C.) feuded with billionaire Elon Musk over the SpaceX CEO’s proposed solution to ending the war in Ukraine in a Twitter thread on Wednesday.

Musk asked his more than 100 million followers on Monday to weigh in on his peace proposal, which includes giving the Crimean Peninsula to Russia and holding new elections in four illegally annexed regions. Ukrainian officials have loudly rejected the idea.

Graham, while acknowledging his “respect” for Musk, shot back on Wednesday that his solution is “dumb” and the world’s richest man needs to “understand the facts of the Russian invasion of Ukraine.”

“In 1994, through the Budapest Memorandum, Ukraine gave up its nuclear weapons arsenal — the third largest in the world — in return for assurances their territorial integrity would be protected,” the senator wrote. “It was an agreement signed by Russia that included protecting Crimea and the Donbas as part of Ukraine.

“If you want peace in Ukraine — which we ALL do — simply demand Russian honor the boundaries they agreed to in 1994 and withdraw their forces,” Graham added. “To do otherwise is to legitimize a bait and switch by Russia and a signal to other bad actors to take what you want – by force! If Elon Musk and others want the world to continue to be in chaos, then by all means capitulate to [Russian President Vladimir] Putin and reward his aggression.”

The senator, among the fiercest critics of Putin in Congress, also mused that lawmakers should “revisit the electric vehicle tax credit” to pay for more assistance to Ukraine in an apparent financial threat to the Tesla CEO.

Musk said that some portions of eastern Ukraine do wish to be a part of Russia.

“Assuming you believe that the will of the people matters, we should, in any given conflict region, support the will of those who live there,” the billionaire wrote, potentially referring recent referenda in the region that have been widely decried as illegitimate.

The spat with the GOP senator adds to a growing list of critics on Musk’s peace proposal. On Monday, a Ukrainian diplomat and Ukrainian President Voldymyr Zelensky sharply criticized the plan.

Musk has provided Starlink satellites to Ukraine to boost internet service amid the war.

The billionaire, who is seeking to revive his $44 billion plan to buy Twitter, also said earlier this year he would start voting Republican.