Sentence:  In 1915, the Supreme Court ruled unanimously in "Guinn v. United States" that grandfather clauses were unconstitutional. ... The decision had almost no effect, however. The Oklahoma Legislature met in special session to <WSD>grandfather</WSD> in the grandfather clause. The new law said those who had been registered in 1914 – whites under the old system – were automatically registered to vote, while African-Americans could only register between April 30 and May 11, 1916, or forever be disenfranchised. That law stayed on the books until a Supreme Court ruling in 1939. 
Meaning of the word marked with <WSD> tags:  To retain existing laws or rules for (a person or organization previously affected by them). (from 1950s)