Strzok, who had worked on the Clinton email investigation, was removed from the Mueller probe in the summer after an inspector general uncovered the texts. But the romantic couple's supposed malign role escalated this week when Sen. Ron Johnson, R-Wis., said a newly released September 2016 text by Page about Obama "may relate" to the Clinton probe.
Analysts said the brief text -- "(the president) wants to know everything we're doing" -- almost certainly referred to preparations for Obama's planned meeting that week with Russian President Vladimir Putin. But conservative commentators seized on the FBI texts as proof of wrongdoing, and Trump tweeted Wednesday that they "are bombshells!"
Much of the right-wing anger has settled on Rosenstein, a Republican who spent 12 years as U.S. attorney in Baltimore, building a solid, uncontroversial reputation as a by-the-books federal prosecutor who poured resources into combating violent crime.
Appointed by Trump to the No. 2 position in the Justice Department, and confirmed by a Senate vote of 94-6, Rosenstein took over the Russia investigation in March when Sessions stepped aside due to questions about his own meetings with a Russian diplomat during the campaign.
After Trump abruptly fired Comey in May, Rosenstein appointed Mueller as special counsel. Since then, Mueller has filed criminal charges against four former Trump aides; two have pleaded guilty, including Trump's former national security adviser, Michael Flynn.
Under Justice Department regulations, Rosenstein has control of the Mueller probe. He can set the budget, determine what Mueller can or can't pursue and, perhaps most importantly, decide whether to make public any final reports. Rosenstein also is the only official empowered to fire Mueller, and has told Congress he would not follow an order to do so without good cause.
Trump likely would face a firestorm of criticism if he sought to fire Mueller. But firing Rosenstein, Mueller's boss, could open the way to naming a more compliant deputy attorney general, one who might rein in Mueller's probe.
Sean Hannity, the Fox News commentator who has been a cheerleader for Trump, has repeatedly called for Rosenstein to resign or be fired. Senate Democrats have warned Trump not to do so, but the president has refused to provide assurances. "You figure that one out," he told reporters last week.
Jenny Beth Martin, a co-founder of Tea Party Patriots, said the Rosenstein ad was produced by a spinoff nonprofit group that spent $100,000 on digital placements. The group does not have to disclose its donors; Martin said most of the money came from small donors reached in a mail campaign.
Under Obama, the tea party group crusaded against Obamacare and for lower taxes. With Republicans now in control of the White House and Congress, Martin said the group is targeting what she called a lack of accountability by career officials like Rosenstein.