The research behind it was funded by Democrats, per the Washington Post:
The Hillary Clinton campaign and the Democratic National Committee helped fund research that resulted in a now-famous dossier containing allegations about President Trump’s connections to Russia and possible coordination between his campaign and the Kremlin, people familiar with the matter said.
Marc E. Elias, a lawyer representing the Clinton campaign and the DNC, retained Fusion GPS, a Washington firm, to conduct the research.
After that, Fusion GPS hired dossier author Christopher Steele, a former British intelligence officer with ties to the FBI and the U.S. intelligence community, according to those people, who spoke on the condition of anonymity.
Elias and his law firm, Perkins Coie, retained the firm in April 2016 on behalf of the Clinton campaign and the DNC. Before that agreement, Fusion GPS’s research into Trump was funded by a still unknown Republican client during the GOP primary.
The Clinton campaign and the DNC, through the law firm, continued to fund Fusion GPS’s research through the end of October 2016, days before Election Day.
And a tart tweet about this story from Maggie Haberman of the Times:
Folks involved in funding this lied about it, and with sanctimony, for a year https://t.co/vXKRV1wRJc
— Maggie Haberman (@maggieNYT) October 24, 2017