Donald Trump has cheered the news that a former adviser to Michael Cohen will testify before a Manhattan grand jury investigating the ex-president’s alleged role in a hush money payment to the adult film star Stormy Daniels. Robert J Costello, a one-time legal adviser to former Trump attorney Cohen, was scheduled to appear before the grand jury on Monday and expected to give testimony “attacking the credibility of Cohen’s statements”, the Associated Press reported. Cohen pleaded guilty in 2018 to federal charges involving $130,000 paid to Daniels close to election day in 2016. Daniels claims she had sex with the former president in 2006, an allegation Trump denies. Trump said on Saturday he would be “arrested on Tuesday” – a claim for which sources close to the 76-year-old said he had no evidence – but then offered a more buoyant outlook after news of Costello’s scheduled appearance. “Just reported that the most important witness to go before the New York City grand jury, a highly respected lawyer who once represented convicted felon, jailbird and serial fake storyteller and liar, Michael Cohen, will be doing so tomorrow afternoon,” Trump wrote on his Truth Social platform. “The information he will present will supposedly be conclusive and irrefutable! Witch hunt!!!” Costello, who has represented the Trump confidants Steve Bannon and Rudy Giuliani, offered to represent Cohen in 2018 as he faced charges related to the Daniels payment. The pair discussed the case, the New York Times reported, but the relationship soured after Cohen began to criticize and implicate Trump. The AP reported that Costello recently contacted a Trump lawyer, claiming he had information that contradicted Cohen’s account and could prove exculpatory for Trump. The lawyer brought it to the attention of the Manhattan district attorney, Alvin Bragg, who last week subpoenaed Costello’s law firm for records and invited him to testify. There was more good news for Trump on Monday when Florida’s governor, Ron DeSantis, his closest rival for the 2024 Republican presidential nomination, addressed the likely indictment for the first time. Trump allies had called for DeSantis to speak out. Speaking to reporters at a college in Panama City, the governor mocked the notion that hush money payments to a porn star might be seen as indictable conduct. He also repeated an antisemitic dogwhistle. DeSantis said Bragg “like other Soros-funded prosecutors, they weaponise their office to impose a political agenda on society at the expense of the rule of law and public safety”. George Soros, a Hungarian American progressive financier and philanthropist, is a boogeyman for Republicans and a regular target for antisemitic invective. DeSantis mentioned “Soros-funded prosecutors” five times in a two-minute answer. Throughout Sunday, Trump published a flurry of all-caps posts, railing against perceived injustice. Using a term short for “Republicans in name only”, one post complained of persecution by “COMMUNISTS, MARXISTS, RINOS AND LOSERS”. Several posts attacked Cohen. While Trump has focused on Bragg, Cohen and others, his lawyers have focused on a defense strategy. Outside counsel – Joe Tacopina and Susan Necheles – have reasoned that a hush money case centered on campaign finance violations could be weak after a similar prosecution against the Democratic senator and vice-presidential nominee John Edwards failed in 2012. If the indictment alleges the Daniels payment violated campaign finance laws, Trump’s lawyers are expected to argue that it fails the “irrespective test” posed by the Edwards case: that Trump would have paid Daniels irrespective of his campaign, to avoid embarrassment because he was a public figure. Trump may face an uphill struggle with those arguments, given that having “mixed motives” to protect himself personally and to protect his campaign could leave him liable. The timing of the payments also suggests an urgency to pay before election day. There is also the matter of Trump’s own comments on the Edwards case. In 2012, he told Fox News “a lot of very good lawyers have told me that the government doesn’t have a good case” against Edwards. As former New York prosecutor Ronn Blitzer wrote for Law and Crime, “that … sentence undermines Trump’s claim that he was relying on Cohen as his attorney to know the law to steer him in the right direction” over the Daniels payment, “and that he didn’t direct Cohen to break the law”. “[Trump] said during the Edwards case that he spoke to ‘a lot of very good lawyers’ about these very issues, which would mean he was aware of the relevant laws,” Blitzer said. Trump’s legal team is also expected to argue that when Daniels tried to sell her story in 2011 she was told to “leave Trump alone – forget the story”, thereby proving her silence was desired long before Trump ran for president. Trump’s lawyers made those arguments when Necheles urged Bragg to drop the case, the Guardian previously reported. But all signs indicate Bragg will move ahead in an unprecedented indictment of a former president – who is also running to return to the Oval Office.