WASHINGTON — The White House and its allies are scrambling for ways to offset potential damage from fired FBI Director James Comey’s highly anticipated congressional testimony, an appearance that could expose new details about his discussions with President Donald Trump about the federal investigation into Russia’s election meddling.

Asked about the testimony, Trump on Tuesday was tight-lipped: “I wish him luck,” he told reporters before a meeting with lawmakers.

Trump’s White House and its allies are crafting a strategy aimed at undermining Comey’s credibility. Both White House officials and an outside group that backs Trump plan to hammer Comey in the coming days for misstatements he made about Democrat Hillary Clinton’s emails during his last appearance on Capitol Hill.

An ad created by the pro-Trump Great America Alliance — a nonprofit “issues” group that isn’t required to disclose its donors —  casts Comey as a “showboat” who was “consumed with election meddling” instead of focusing on combating terrorism. The 30-second spot is slated to run digitally on Wednesday and appear the next day on CNN and Fox News.

The Republican National Committee has been preparing talking points ahead of the hearing, which will be aired live on multiple TV stations. An RNC research email Monday issued a challenge to the lawmakers who will question Comey. There’s bipartisan agreement, the email says, that Comey “needs to answer a simple question about his conversations with President Trump: If you were so concerned, why didn’t you act on it or notify Congress?”

Comey’s testimony before the Senate intelligence committee marks his first public comments since he was abruptly ousted by Trump on May 9. Since then, Trump and Comey allies have traded competing narratives about their interactions. The president asserted that Comey told him three times that he was not personally under investigation, while the former director’s associates allege Trump asked Comey if he could back off an investigation into Michael Flynn, who was fired as national security adviser because he misled the White House about his ties to Russia.

Democrats have accused Trump of firing Comey to upend the FBI’s Russia probe, which focused in large part on whether campaign aides coordinated with Moscow to hack Democratic groups during the election. Days after Comey’s firing, the Justice Department appointed a special counsel, former FBI Director Robert Mueller, to oversee the federal investigation.

Despite the mounting legal questions now shadowing the White House, Trump has needled Comey publicly. In a tweet days after the firing, he appeared to warn Comey that he might have recordings of their private discussions, something the White House has neither confirmed nor denied.