ACLU through their own eyes...

The ACLU was founded in 1920

It’s purpose,they claim "IS to challenge governments, to make sure that the Bill of Rights and it’s principles are protected". The American system of government is founded on two counterbalancing principles: that the majority of the people governs, through democratically elected representatives; and that the power even of a democratic majority must be limited, to ensure individual rights.

Majority power is limited by the Constitution's Bill of Rights, which consists of the original ten amendments ratified in 1791, plus the three post-Civil War amendments (the 13th, 14th and 15th) and the 19th Amendment (women's suffrage), adopted in 1920.

The mission of the ACLU is to preserve all of these protections and guarantees:

Your First Amendment rights - freedom of speech, association and assembly; freedom of the press, and freedom of religion.
Your right to equal protection under the law - equal treatment regardless of race, sex, religion or national origin.
Your right to due process - fair treatment by the government whenever the loss of your liberty or property is at stake.
Your right to privacy - freedom from unwarranted government intrusion into your personal and private affairs.

"we work also to extend rights to segments of our population that have traditionally been denied their rights, including Native Americans and other people of color; lesbians, gay men, bisexuals and transgender people; women; mental-health patients; prisoners; people with disabilities; and the poor."
If the rights of society's most vulnerable members are denied, everybody's rights are imperiled.

The ACLU was founded by Roger Baldwin, Crystal Eastman, Albert DeSilver and others in 1920. We are nonprofit and nonpartisan and have grown from a roomful of civil liberties activists to an organization of more than 500,000 members and supporters. We handle nearly 6,000 court cases annually from our offices in almost every state.
The ACLU has maintained the position that civil liberties must be respected, even in times of national emergency. The ACLU is supported by annual dues and contributions from its members, plus grants from private foundations and individuals. We do not receive any government funding.

The ACLU soon established its reputation by defending victims of the harsh Palmer Raids and taking on First Amendment cases having to do with free speech and religious liberty,

Roger Nash Baldwin-co-founder's personality was typical of a 1920s civil libertarian: An ardent pacifist who opposed World War I, he was also a communist for most of his early life, writing a book in 1927 on what he saw as the young Soviet Union's considerable potential to become a shining beacon of human rights. When the emergence of Stalin and the signing of the Nazi-Soviet Pact made it clear that this would not happen, Baldwin denounced communism.

Elizabeth Gurley Flynn 1940 expulsion of Elizabeth Gurley Flynn, a member of the ACLU's Board of Directors who openly belonged to the American Communist Party. The American Communists had by that point favored peace and neutrality in international relations, but this did not matter to Baldwin, who felt--presumably with a convert's zeal--that no Communist could be a civil libertarian. Flynn's removal from the ACLU board, more than a decade before.

Patick Murphy Malin-Malin (1950-63) Malin was phenomenally successful at building membership--from about 8,000 to about 60,000--by creating a powerful network of local ACLU activist communities.He failed to adequately protect Americans targeted by Joseph McCarthy and others during the second Red Scare, and even went so far as to leak private ACLU documents to J. Edgar Hoover in exchange for FBI surveillance information on political affiliations of Board members. Malin had presumably hoped to avoid the embarassment of having any ACLU board members outed as communists by McCarthy.

The defining conflict of the ACLU during the 1950s was between Malin and Corliss Lamont, a member of the ACLU Board of Directors who had written a 1952 book titled The Myth of Soviet Aggression. Although Lamont was not a member of the American Communist Party, he was targeted by McCarthy and received no substantial support from the ACLU.

By the end of Malin's tenure, the ACLU had become a largely irrelevant, moderate force in American policy. Beloved by many but feared by few, it took the correct positions on some issues--most notably filing an amicus brief against school segregation in the landmark Brown v. Board of Education (1954)--but was hardly the fearsome defender of civil liberties that it had once been, and would soon become again.