Yes, because Utah was still a territory, the Federal government had broad powers over the area. The Edmunds Act, one of a series of anti-polygamy laws, made polygamy a felony in US territories. It also made unlawful cohabitation a misdemeanor, since proving that actual marriages took place was difficult.
In addition, it made it illegal for polygamist or cohabitants to vote, hold public offices or serve on juries. They enforced these restrictions against people who stated a belief in the doctrine regardless of whether the person was actually practicing it or not.
In one famous case,
During the late 1880s, when the federal government was very active in prosecuting polygamists, Brown attempted to get himself seated on a federal grand jury. Brown was never himself a polygamist, but as a devoted member of the church he could try to ensure a sympathetic voice was present on the grand jury. As part of jury selection, he was asked if he believed in polygamy, and he said that he did not. This resulted in him being tried for perjury, where in his defense he said that he had a knowledge, not mere belief, that polygamy was a true principle. He was convicted and sentenced to three years in prison and a $1000 fine.
Trivia time: The prison at the time was the Sugar House Penitentiary, located at what in now Sugar House Park.
One of the famous cases of men convicted of polygamy was Rudger Clawson, who became an apostle and later the President of the Quorum of the Twelve Apostles.
As an apostle, he married his third wife in 1904, after not only the 1890 Manifesto but also after the Second Manifesto promising that the LDS Church really, really, really isn’t practicing polygamy.
That same year, Clawson secretly contracted a plural marriage with Pearl Udall, daughter of David King Udall and Eliza Stewart Udall.[3][4][5][6][7] Because they married after then-church president Joseph F. Smith issued a manifesto expressly prohibiting plural marriage among Latter-day Saints,[8] their relationship was a “clandestine marriage of secret meetings and long absences”, and they never shared a home. After discussing their marriage across several rendezvous held in the three-month span of October 1912 to January 1913, Clawson “released her [Pearl Udall] from the marriage”, and they ceased to live as spouses.[9]
As an apostle, he was in the senior leadership and yet took a polygamous marriage in direct defiance to a direction from the president of the church.
At this stage of Mormonism, polygamy was its defining doctrine. It had been openly taught for 40 years and the covertly taught for another 10 that they must practice this here, on Earth in order to become gods and goddesses in the next life.
Mormons had gone to war with the US government over the issue. They were supposed to be all in, and they were expected an appocolypse and the second coming Christ to come any day, and it was their job to prepare the world for His return.
It would have been like the US going communist in the 60s. Absolutely unbelievable and unacceptable.
Some people couldn’t accept the end of polygmany and broke off, becoming the fundamentalist movement that later gave the FLDS and other sects. Many of those joining were for members of the first or second tier of leadership, so they would know or hear about continued polygamy at the top.
Dissenters pointed out that the Manifestos were never presented as revelations and also claimed there were secret revelations commanding them to continue. In particular, there was one from John Taylor, the successor to Brigham Young, in which is said that God would never revoke polygamy.
And as I have heretofore said by my servant Joseph: all those who would enter into my glory must and shall obey my law [of polygamy] and have I not commanded men, that if they were Abraham’s seed and would enter into my glory, they must do the works of Abraham? I have not revoked this law, nor will I, for it is everlasting and those who will enter into my glory must obey the conditions thereof.
While the LDS Church long denied the existence of this revelation, they quietly added it to the archive of digitalized records this summer.