Revision ceca15b4-89dc-4a8c-83f2-7d99b3670fd2 - Code Golf Stack Exchange

#JavaScript (ES6), <s>231</s> <s>227</s> <s>223</s> <s>221</s> <s>210</s> 207 bytes

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 _=>["Socialist","Trade Unionist","Jew"].map(x=>s+=t+`the ${x}s, and I did not speak out-
 Because I was not a ${x}.
 
 Then`,s="",t=` they came for `)&&`First${s+t}me-and there was no one left to speak for me.`

---
##Try it

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

 o.innerText=(
 _=>["Socialist","Trade Unionist","Jew"].map(x=>s+=t+`the ${x}s, and I did not speak out-
 Because I was not a ${x}.
 
 Then`,s="",t=` they came for `)&&`First${s+t}me-and there was no one left to speak for me.`
 )()

<!-- language: lang-html -->

 <pre id=o>

<!-- end snippet -->

---
##Original, 221 bytes

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

 o.innerText=(
 _=>`First${t=" they came for "}the Socialist${a=`,s and I did not speak out-
 Because I was not a `}Socialist${t=`.

 Then`+t}the ${(u="Trade Unionist")+a+u+t}the Jew${a}Jew${t}me-and there was no one left to speak for me.`
 )()

<!-- language: lang-html -->

 <pre id=o>

<!-- end snippet -->