Story highlights Comey is set to testify Thursday on his interactions with Trump

The spot will air on national television on Thursday during the hearing

Washington (CNN) A pro-Trump outside group is seeking to label James Comey as untrustworthy ahead of the former FBI director's scheduled testimony on Capitol Hill on Thursday.

The nonprofit Great America Alliance said Tuesday it would air an ad calling Comey "just another DC insider only in it for himself." The spot, called "Showboat," takes its name from something President Donald Trump himself has called Comey

The ad reflects Trump's attempts to convince Americans that Comey is not credible.

Comey is set to testify Thursday before the Senate intelligence committee about his interactions with Trump, whose associates Comey was investigating before Trump fired him from his position atop the bureau last month. Reports have emerged since that Trump sought to pressure Comey to drop his scrutiny of aide Michael Flynn's ties to Russia, a charge Trump has denied.

The spot will air on national television during the hearing, and on digital platforms before then. It has $400,000 behind it, the group said.

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