Each act, each occasion, is worse than the last, but only a little worse. You wait for the next and the next. You wait for one great shocking occasion, thinking that others, when such a shock comes, will join with you in resisting somehow. You don't want to act, or even talk, alone; you don't want to 'go out of your way to make trouble.' Why not?-Well, you are not in the habit of doing it. And it is not just fear, fear of standing alone, that restrains you; it is also genuine uncertainty. Uncertainty is a very important factor, and, instead of decreasing as time goes on, it grows. Outside, in the streets, in the general community, 'everyone' is happy. One hears no protest, and certainly sees none. You know, in France or Italy there would be slogans against the government painted on walls and fences; in Germany, outside the great cities, perhaps, there is not even this. In the university community, in your own community, you speak privately to your colleagues, some of whom certainly feel as you do; but what do they say? They say, 'It's not so bad' or 'You're seeing things' or 'You're an alarmist.'

And you are an alarmist. You are saying that this must lead to this, and you can't prove it. These are the beginnings, yes; but how do you know for sure when you don't know the end, and how do you know, or even surmise, the end? On the one hand, your enemies, the law, the regime, the Party, intimidate you. On the other, your colleagues pooh-pooh you as pessimistic or even neurotic. You are left with your close friends, who are, naturally, people who have always thought as you have....

But the one great shocking occasion, when tens or hundreds or thousands will join with you, never comes. That's the difficulty. If the last and worst act of the whole regime had come immediately after the first and smallest, thousands, yes, millions would have been sufficiently shocked-if, let us say, the gassing of the Jews in '43 had come immediately after the 'German Firm' stickers on the windows of non-Jewish shops in '33. But of course this isn't the way it happens. In between come all the hundreds of little steps, some of them imperceptible, each of them preparing you not to be shocked by the next. Step C is not so much worse than Step B, and, if you did not make a stand at Step B, why should you at Step C? And so on to Step D.

And one day, too late, your principles, if you were ever sensible of them, all rush in upon you. The burden of self-deception has grown too heavy, and some minor incident, in my case my little boy, hardly more than a baby, saying 'Jewish swine,' collapses it all at once, and you see that everything, everything, has changed and changed completely under your nose. The world you live in-your nation, your people-is not the world you were born in at all. The forms are all there, all untouched, all reassuring, the houses, the shops, the jobs, the mealtimes, the visits, the concerts, the cinema, the holidays. But the spirit, which you never noticed because you made the lifelong mistake of identifying it with the forms, is changed. Now you live in a world of hate and fear, and the people who hate and fear do not even know it themselves; when everyone is transformed, no one is transformed. Now you live in a system which rules without responsibility even to God. The system itself could not have intended this in the beginning, but in order to sustain itself it was compelled to go all the way."

Back in 1950, when both major parties were broad and moderate with overlapping appeals, many of America’s leading political scientists wrote a report in which they bemoaned this state of affairs.

In a report, “Toward a More Responsible Two-Party System,” they saw two national parties that were but loose confederations of state and local parties, incapable of bringing forward coherent programs to the voters and carrying them out when they got into power.

If the American political parties failed to heed their advice, the authors issued a dire warning:

If the two parties do not develop alternative programs that can be executed, the voter’s frustration and the mounting ambiguities of national policy might also set in motion more extreme tendencies to the political left and the political right. This, again, would represent a condition to which neither our political institutions nor our civic habits are adapted. Once a deep political cleavage develops between opposing groups, each group naturally works to keep it deep. Such groups may gravitate beyond the confines of the American system of government and its democratic institutions.

Assuming a survival of the two-party system in form though not in spirit, even if only one of the diametrically opposite parties comes to flirt with unconstitutional means and ends, the consequences would be serious. For then the constitution-minded electorate would be virtually reduced to a one-party system with no practical alternative to holding to the “safe” party at all cost.

(That being said, this quote does show some age, as we now know that this "constitution-minded electorate" doesn't really exist. And "moderate" is extremely relative)