What does the cause for your feeling like “downing a quart of Red Bull” mean?

Solution 1:

Cause for downing a drink is not the same as you feel like downing it. I may feel like a drink without any particular reason **, but saying I have cause for a drink implies that I need it, perhaps because of bad news, Red Bull is famously marketed as giving energy, so the metaphor means that the decision left Republicans needing something to give them the strength to go on campaigning. It's a bit strained, and I can't see it ever becoming 'a popular phrase', but no doubt regular readers will take the point.

** If all be true that I do think/ There are five reasons why we drink;/ Good wine, a friend, or being dry,/ Or lest we should be by and by;/ Or any other reason why.

Solution 2:

In US political analysis, there is a phrase energize the base which means to stir up or inspire those who are your most fervent ideological supporters to further action.

The Roberts' decision on the Affordable Care Act, often called Obamacare by its opponents (and sometimes its supporters, including President Obama) has upset many Republicans. The quote is seeking to indicate that the decision may be likely to stir up many of those most ideologocially opposed to the legislation, and spur them to action. For example, this story discusses energizing the base in connection with the Roberts' decision.

Red Bull is an energy drink. It is usually sold in small cans (much less than a quart). The metaphor indicates that many Republicans may act as if they have have drunk many of the small cans and are now raring to go to overturn the Act. It may also imply that those opponents may need to make an extreme effort to stir up action, by getting themselves in motion.

Alcoholic beverages would not have the desired effect. This is not a "drowning your sorrows" comment.

I do not believe that "downing a quart of Red Bull" is a common phrase, but reference to Red Bull when describing someone who is agitated is, similar to suggesting someone has drunk too many cups of coffee.

Solution 3:

To "feel like downing a quart of Red Bull" means that you feel the need to drink a large quantity of a "restorative."

Because you are very upset about something (Republicans about "conservative" Justice Roberts' support of Obamacare).

It doesn't "have" to be Red Bull. Whiskey, vodka or beer might do fine. But not juice or water.