Isn't this just sour grapes whenever a Democrat is in the White House?

No. Texas independence is not a mood, and it is not tied to which party holds Washington. The movement was here before the current administration, it will be here after the next one, and the case for it does not change color with the party in power. The problem is the size and distance of the federal government itself, and that does not improve when your team wins.

The case is structural, not partisan

The argument for independence has nothing to do with who sits in the Oval Office. Texans send hundreds of billions of dollars to Washington every year and watch a shrinking share come back with strings attached. The federal debt climbs past anything that can be seriously repaid. The decisions that shape life in Texas are made farther and farther from Texas. None of that is fixed by a change of administration. A new president does not shrink the debt, return the money, or move the decisions closer to home. The machine runs the same regardless of who is nominally driving.

"Your side wins sometimes" is exactly the trap

The whole promise of the federal system is that you get your turn. Win the right elections and Washington will work for you. Texans have run that experiment for generations, under presidents of both parties, and the federal government grew under all of them. When your party holds Washington, the spending and the centralizing do not stop. They just get aimed at different targets. The lesson is not "wait for the next election." The lesson is that the structure produces the same result no matter who is in charge. You cannot vote your way out of a system in which Texas is permanently outnumbered.

Independence is not about escaping one president. It is about self-government

The point of Texas independence is not to dodge a particular administration for four years. It is to put the decisions that affect Texans in the hands of Texans, permanently, so the answer to "who governs Texas" stops depending on a coin flip every four years in another part of the country. That is a goal that does not expire when a term ends. A Texan who only wants independence when the other party wins has not understood the argument. A Texan who wants it no matter who is in power has.

The accusation is a way to avoid the question

Notice what the "sour grapes" line is built to do. It changes the subject. Instead of answering whether Texas can govern itself, whether Texans are overtaxed by Washington, or whether the people deserve a vote, it dismisses the whole thing as a tantrum so the actual questions never get asked. It is easier to call a Texan a sore loser than to explain why Texans should not be allowed to vote on their own future. When the response to "let the people decide" is "you are just upset," the person saying it has run out of reasons.

The bottom line

This is not sour grapes. It is the considered position that Texas should govern Texas, and that position holds whether the president has an R or a D next to the name. The federal government is too big, too far, and too indebted to fix from the inside, and that is true every January no matter who takes the oath.