Monday marks a pivotal moment in Donald Trump’s hush money trial as Michael Cohen, Trump’s former lawyer and confidant, prepares to take the stand. Cohen’s anticipated testimony holds significant weight in what is the first criminal case against an American president, with its outcome likely to be influenced by his words.

As the star prosecution witness, Cohen’s appearance underscores the trial’s progression into its crucial phase. Manhattan district attorney’s office views Cohen’s testimony as central to their case, aiming to conclude their evidence presentation by week’s end.

Cohen is expected to shed light on his involvement in orchestrating hush money payments during Trump’s initial presidential campaign. These payments, including one to adult film star Stormy Daniels, form a key aspect of the trial. Daniels testified last week, detailing the $130,000 payment she received in 2016 to silence her about an alleged decade-old sexual encounter with Trump in a hotel suite.

Cohen’s significance extends beyond his testimony, as the reimbursements he received are pivotal in the case against Trump. The charges against Trump, comprising 34 felony counts of falsifying business records, are rooted in these reimbursements. Prosecutors contend that these payments were improperly categorized as legal expenses to mask their true nature.

Anticipating Cohen’s testimony, defense attorneys have signaled a vigorous cross-examination. They’ve portrayed Cohen as an “admitted liar” driven by a personal vendetta against Trump. They allege that Cohen’s motivations stem from an “obsession to get President Trump.”

The forthcoming testimony of a witness privy to such intricate details of Trump’s actions may amplify the legal jeopardy facing the presumptive Republican presidential nominee, contingent upon jurors’ perception of his credibility. However, from a political standpoint, prosecutors’ reliance on a witness with a tarnished past—given Cohen’s guilty plea to federal charges related to the payments and lying to Congress—could provide Trump with a strategic advantage. Trump has seized upon this narrative to galvanize fundraising efforts and portray the case as emblematic of a flawed criminal justice system.

Nonetheless, Cohen’s pivotal role as the prosecution’s star witness underscores the demise of a once close and symbiotic relationship. Cohen, who once famously proclaimed his willingness to “take a bullet for Trump,” now finds himself testifying against his former ally. Following the FBI raid on Cohen’s residence and office in 2018, Trump initially expressed support for Cohen, lauding him on social media as a “fine person with a wonderful family” and incorrectly predicting that Cohen would not “flip.”