Secession is unconstitutional. See Texas v. White, 74 U.S. 700 (1868)
Rachel Kleinfeld at The Hill:
Rep. Marjorie Taylor Greene (R-Ga.) is far from the only politician interested in secession, which has been discussed by the Wyoming GOP chairman and is already part of the Texas GOP platform.
While the right is more vocal, a national breakup is not its dream alone. A June 2021 survey by Bright Line Watch found about a third of the country supported a split. Their ranks include more than half of Southern Republicans, but also 41 percent of Democrats in California and the Pacific Northwest, and 34 percent of heartland independents.
Whatever America was left would have a rump military. As the most populous state, California supplies the largest number of U.S. service members, but Texas and other Southern states provide the bulk of the military force. The South hosts a disproportionate number of bases. Who would get what? However things were split, the winners would be China and Russia, which would face a hobbled United States.
Perhaps that is why Russia has been the biggest supporter of secession talk in the United States. Californians who wanted out might be surprised that one of the Republican operatives leading the referendum had deep, longstanding ties to Russia and returned to live there before California’s referendum was even complete. The most popular Texas secession page on Facebook was created not by Lone Star defenders but Russian trolls.
The Kremlin has supported secessionist efforts worldwide to weaken democracies — from the Catalans in Spain to Scottish independence. In 2016, it sponsored a conference for global secessionist movements — including Texas, California and Puerto Rico.