The dossier has become a focus for Republicans seeking to discredit the investigation into Trump’s ties to Russia. Some critics have argued that the entire investigation was premised entirely on Steele’s work, which elicited a rebuttal laying out how the probe long predated the dossier.

Focusing on the Page warrant is a surprising strategy. It is not difficult to imagine that the American intelligence community had more information about Page than what was in the Steele dossier. As early as 2013, the U.S. government believed Russian intelligence was trying to recruit Page as an asset. The FBI was also surveilling him in 2016, prior to any warrant request that Rosenstein would have approved.

While illegally obtained evidence is indeed invalid, Page makes for an unlikely rallying point, both because of his history of questionable ties to Russia and because of his own statements in interviews and in congressional hearings. In jaw-dropping November 2 testimony to the House Intelligence Committee, Page offered confusing and often changing testimony about trips to Russia and Hungary and about who he had met with during those trips.

Page is a particularly unusual foil for Rosenstein, who until joining the Trump administration had a reputation as a meticulous, nonpartisan, and fair public servant but is also a lifelong Republican. But the deputy attorney general has found himself a medium for partisan warfare. After Attorney General Jeff Sessions recused himself from the Russia investigation, Rosenstein inherited it, and soon appointed Robert Mueller as special counsel.

Although Rosenstein is a Republican and was appointed to his post by Donald Trump, the president has suggested he is a Democrat and questioned whether he is trustworthy. The crux of Trump’s anger is the Mueller investigation: Trump is angry about Mueller’s appointment, and angry that Rosenstein has endorsed Mueller’s work so far. Trump has railed against Rosenstein in interviews, and according to a New York Times story last week considered firing him as a method of firing Mueller.

Attacking Rosenstein serves a dual purpose for Trump and his allies. If Rosenstein is forced to resign or fired, Trump would appoint a replacement who would become Mueller’s boss, and could fire the special counsel or move to limit his probe. The White House seems to recognize that firing Rosenstein merely to mess with the Mueller probe would be politically disastrous, but alleging misconduct in a warrant application could provide an excuse to push him out for other reasons. Even if Rosenstein doesn’t go, however, the current line of argument serves the purpose of undermining trust in the FBI and DOJ as they continue to investigate Trump.

Last week, it was revealed that Trump sought to fire Mueller in June, but was blocked by White House Counsel Don McGahn, who threatened to resign rather than order Mueller’s dismissal. Trump has at times threatened to fire Mueller, and a pivotal moment is approaching, as Mueller talks with Trump’s attorneys about the president testifying. Democrats and some Republicans have renewed warnings to the White House not to fire Mueller, but bills that would protect the probe have bogged down in Congress.