Being transgender is about gender identity (who you are). Being L, G, or B is about sexual orientation (who you are attracted to). A trans person can be straight, gay, lesbian, bisexual, etc.
This shared history created a foundation of solidarity. Transgender people provided the "radical" spark that demanded more than just tolerance; they demanded the right to exist authentically in public spaces. The "T" in the Umbrella: Identity vs. Orientation
Historically, some segments of the LGB community attempted to distance themselves from trans people to appear more "palatable" to mainstream society. The infamous "LGB without the T" movement of the 1990s and early 2000s was a failed attempt to secure rights for gays and lesbians by throwing trans people under the bus. It failed not only morally but strategically—today, the consensus within queer activism is clear: