The omnibus bills aren’t blackmail, as much as a symptom of the failure of Congress to be able to do what it is supposed to: debate.

There is 1 funding bill per year which only requires a 50% vote instead of a 60% / 67% to pass that all other spending bills require.

Every member with a goal tries to attach it to the big annual funding bill. The bill becomes so large that nobody likes the bill as a whole, but everybody has something in it they will defend.

And the old filtering process (committees which recommend the content of bills) are dominated by majority party leadership. This is maybe the closest symptom to blackmail.

I‘m not (yet) a citizen of the USA, but I’ve lived there for a while. As I understand it, there is hardly any political opposition in this country. I would actually describe it as a controlled opposition. A lot of people here tend to think the only role of the opposition is to run the right candidate and win the next election. As such, there is no real resistance when the majority government oversteps their boundaries.

To make matters worse, labor unions are equally politically inactive, and most often their only political moves are endorsing candidates. When they do voice support for or opposition against bills, those bills are often stuff related to their industry, and seldom do they actually oppose an over reaching government by threatening general strikes etc.

The press here is also very right leaning. All the big media are owned by capitalist conglomerates and as such most people never hear real challenges to the capitalist power structure. As long as the government class acts favorable to the capitalist interest, then the press has aligning interest, and is thus heavily incentivized to never challenge the government to much.