Around 300 demonstrators waved shoes in front of the president's official residence in Berlin on Saturday, in a protest modelled on of those in the Arab world, where waving shoes is a sign of disrespect and anger.
As new revelations emerge almost daily about Wulff, a member of Merkel's Christian Democratic Union (CDU), a senior member of the opposition Social Democratic Party (SPD) sought to shift the heat onto Merkel.
The SPD's parliamentary group leader former foreign minister Frank-Walter Steinmeier, noted that Merkel had pushed through Wulff's election to the largely ceremonial post in 2010.
"She cannot just act as if she has nothing to do with this whole affair and as if the federal president is in a different political sphere," Steinmeier told Sunday's edition of the Tagesspiegel.
And the SPD general, Andrea Nahles, told the Bild am Sonntag weekly: "If Wulff resigns, then there should be new elections ... the Wulff affair is also a Merkel affair."
"Christian Wulff is not up to the office of federal president. Staying in office, no matter what happens? That behaviour is not acceptable ... I have serious doubts that he will survive this affair," added Nahles.
The scandal broke in December when the mass circulation Bild reported that Wulff had failed to declare a €500,000 loan he had obtained from the wife of a wealthy tycoon while he was the Lower Saxony state premier.
On learning the story was about to break, Wulff called the paper's editor, leaving a furious voicemail message, and also called chief executive of the paper's publisher Springer.
According to the Der Spiegel news weekly, Wulff asked to discuss the story on his return from an official trip "and then we can decide how we see things and then we can decide how we should wage war."
Wulff failed to put the scandal to bed with a televised interview last week – his claim that he asked Bild to delay the story rather than stop it altogether was challenged by the paper.
As recently as Friday, Merkel's spokesman said she had "great esteem" for Wulff both as a person and as a president, but the scandal is an increasingly unwelcome distraction as she seeks to focus on the eurozone debt crisis.
Top government officials scrambled to deny reports over the weekend that talks had taken place over a possible successor to Wulff.
However, as hundreds protested outside the official presidential residence in Berlin over the weekend and polls on Sunday showing Germans believed he had lost credibility, Wulff himself reportedly sought to shrug off the scandal.
"In a year, this will all be forgotten," he told staff members, according to the Bild am Sonntag newspaper.