The email presents an overview of all the new districts (with some trivial inaccuracies) of which the most relevant comments are those involving districts 24 and 26. As described at Political State Report, "the email is notable for the blunt way in which it addresses the way in which minorities were shunted from district to district, squeezing them out of districts to favor republicans where the vote was close, or else putting them into overwhelmingly republican districts where their voting power would be diluted."
This email alongside additional circumstances - Rep. DeLay's involvement, statements by GOP legislators regarding their overtly partisan intent, the subordination of 'traditional' districting principles (most notably communities of interest and protecting incumbent seniority) - leave no doubt as to motivations underlying the process. As one might imagine, this is a fairly key aspect toward establishing the factual circumstances upon which any challenges might be decided (it also closely parallels the 2002 Pennsylvania process, BTW).
As alluded, the Supreme Court has ruled previously (most prominently in a ruling involving employment discrimination against Republicans in West Virginia) that political viewpoint-based discrimination is prohibited by the First Amendment. As mentioned, the Supreme Court has never extended this doctrine to the redistricting process, and it's by no means assured that it will ever do so. My point in citing the memo and alluding to these other factors is simply that in the event that the Vieth v Jubelirer ruling is based in any part on that basis, the Texas mapping process is particularly susceptible.
More likely in my opinion, the maps will be struck down for a combination of racial gerrymander and minority retrogression. The map is vulnerable to such a reversal in several respects which are most easily reviewed in the brief filed challenging the maps. There is also the Article I issue of re-redistricting as well as the partisan gerrymander challenge pursuant Davis v Bandemer also covered in this challenge that may potentially lead to an overturning of these maps. The one element where this map does not appear vulnerable is the majoritarian principle which provides the crux of the Vieth challenge.
My basic point is that any court inclined to favor the Democrats will have no problem identifying sufficient grounds to strike down this process.
This map diminishes the number of congressmen that the Democrats will elect. That's indisputable, but not surprising. What's also indisputable is that the map, as a whole, creates more minority opportunity districts, and that more minorities will represent Texas (and be Democrats, too) under this new map than under the old one which Democrats created.
Minorities do not get a bad deal under this map, unless you adopt the Democrats' apparent argument that all minorities have the constitutional right to be represented only by Democrats.