They have refused to vote appropriations for protecting Texas against ruthless savages, for the sole reason that she is a slave-holding State.(Emphasis yours.)
I'm not sure you make your point the way you wanted it to be taken. That is, yes, the Texans are arguing that the Northern States' congressional representatives, in denying the military appropriation, made it clear that their reason for doing so, was that Texas was a slave State. It was the Northern politicians who made slavery the issue, when the issue Texas took with their having done that, was that it was a violation of the Constitution, viz., denying Texans the protection of federal troops, which was still extended to other States that were in better political odor with the Northern political faction.
Which is pretty much how the whole issue of slavery came to the fore in the first place. The Abolitionists made it an issue, and the Republican Party took up the cudgels for their own, somewhat different reasons.
There has been some recent scholarship on the subject of the Northern moral crusade against slavery, its content and the method and tenor of its propagation, that tells us a good deal about how the issue came to be such a large one.
Remember, slavery wasn't the issue in 1832 when North and South clashed over the 1828 Tariff. It was Northern politicians who sought to make it a sectional issue, and attached the slavery crusade to it (being a moral crusade, and therefore absolute, its appeal could never be appeased except by the destruction of its object), the better to unite their advantage in numbers, consolidate the North with the agrarian Midwest, and overwhelm their opponents in the Congress and take over the federal government, which at length they did, after the slavery issue neutralized Northern exponents of the National Democracy like Stephen Douglas. Douglas had been a viable future presidential candidate when he helped engineer the 1850 Compromise, but his political career was utterly destroyed by the slavery issue and Kansas-Nebraska. Kansas-Nebraska was his effort to straddle and finesse the slavery issue being pushed by Free Soilers and Northern Whigs. Lincoln not only unhorsed Douglas but wrecked his party with the slavery issue.
That is why slavery was an issue in 1860: because the Republicans and Free Soilers insisted on making it the paramount issue, when thanks to Henry Clay and the 1820 Missouri Compromise, it hadn't been before Texas's (denied) application for statehood in 1836. The territorial gains of Texas annexation and the Mexican War required it to be put to bed again with the 1850 Compromise, but after Kansas-Nebraska and Dred Scott, Lincoln and the Republicans set sail on a policy of "no victory, no peace", when Lincoln gave the 1858 "House Divided" speech, the implications of which were clear: that no matter what he said about the extension of slavery, Lincoln was committed to the extinction of slavery, and therefore the extinction of the cotton economy and with it the livelihood of the agrarian South.
Then I assume you won't have any trouble pointing to some of those Northern States' congressional representatives making that clear, right?
The fact is that about a full 25% of the Army was on the Texas frontier in the decade before secession, vastly larger, proportionately, than the percentage of the armed forces in Iraq at the height of the surge.
Douglas had been a viable future presidential candidate when he helped engineer the 1850 Compromise, but his political career was utterly destroyed by the slavery issue and Kansas-Nebraska. Kansas-Nebraska was his effort to straddle and finesse the slavery issue being pushed by Free Soilers and Northern Whigs. Lincoln not only unhorsed Douglas but wrecked his party with the slavery issue.
You are aware, right, that Lincoln lost to Douglas in the 1858 senate race, four years after you say his political career was "utterly destroyed" by the Kansas-Nebraska Act?
I'd say you're fantasizing.
When Texas seceded, "Doughfaced" Democrat James Buchanan was President, and Colonel Robert E. Lee was in charge of protecting Texas.
In Buchanan's cabinet were:
Sorry, but the whole idea that the South had somehow been "oppressed" or "ignored" by Washington is just rubbish and nonsense.