I think if you look back at the Strzok/Paige/Comey messages they were planting the seeds on this long before December. Can’t remember when they first mentioned Russia specifically but looking back they were obviously cooking this up long before December in an attempt to prevent Trump’s election.
Just found a timeline going all the way back to June.
During the Republican presidential primary contest, The Washington Free Beacon hired Fusion GPS to conduct opposition research on multiple candidates, including Donald Trump. Knowing that the law firm Perkins Coie represented the Democratic National Committee (DNC) and Hillary Clinton’s campaign, Fusion GPS approached Perkins Coie and offered to continue the opposition research on Donald Trump that it had begun with The Washington Free Beacon . Together, the DNC and the Clinton campaign paid Fusion GPS $1.02 million for those services via Perkins Coie., 
In June of 2016, Fusion GPS hired former British intelligence officer Christopher Steele and his London-based firm, Orbis Business Intelligence, to investigate Donald Trump’s ties to Russia. Working for Fusion GPS between June and November of 2016, and relying upon information from Russian contacts, Steele drafted 17 memoranda that were compiled into a 35 page document commonly referred to by the media as “the Russia Dossier,” “the Trump Dossier,” and “the Steele Dossier.”
Published June 20, Steele’s first memorandum alleged that the “Russian regime has been cultivating, supporting and assisting TRUMP for at least 5 years”; that Trump has “accepted a regular flow of intelligence from the Kremlin, including on his Democratic and other political rivals”; and the Russian Federal Security Service (FSB, formerly KGB) has “compromised TRUMP through his activities in Moscow sufficiently to be able to blackmail him.” Among these are “perverted sexual acts which have been arranged/monitored by the FSB.” Also, the Russian Intelligence Services had compiled a dossier on Hillary Clinton comprised mostly of bugged conversations and intercepted phone calls. This “dossier is controlled by Kremlin spokesman, PESKOV, directly on PUTIN’s orders.”
On July 5—the same day as then-FBI Director James Comey’s news conference exonerating Hillary Clinton—Christopher Steele provided his research to an FBI contact in Europe. He also presented his research to British intelligence. Later that month, then-Deputy Head of Counterintelligence Peter Strzok began supervising a probe into Russian interference in the 2016 U.S. presidential election process, including possible collusion with the Trump campaign.,