Grassley's decision to put the brakes on Mateer's nomination is unique, particularly considering how quickly he has moved to seat other Trump judicial nominees, even those that have courted controversy or come under intense criticism from Democrats.
The White House didn't respond to a request for comment on the derailed picks or what went wrong, but Mr. Grassley said he didn't think there was a breakdown in the Senate's own vetting process.
Grassley told CNN the White House should "reconsider" the nomination of Jeff Mateer for a district judgeship in Texas and "should not proceed" on the nomination of Brett Talley for a district court vacancy in Alabama.
"I've advised the White House they ought to reconsider", Grassley said as he left a Judiciary Committee hearing.
It's unclear whether Senate Majority Leader Mitch McConnell will ultimately schedule a floor vote for Talley.More news: Celebrate Hanukkah with these traditional foods
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On Wednesday, a Trump administration official told NPR that Talley's judicial appointment "will not be moving forward". But Talley's nomination to the U.S. District Court for the Middle District of Alabama has been riddled with problems from the beginning.
Buzzfeed reported that Talley first offered to withdraw last week. He called transgender children part of 'Satan's plan.' There is absolutely no way any member of the LGBTQ community could expect fair judgement in any court with Mateer on the bench.
Mateer has run into trouble over speeches he made in 2015.
Last month, Sen. John Kennedy (R-La.) was the first Republican to raise problems with Talley, saying he would vote against his confirmation because he's "never tried a lawsuit in his natural life ..." So far this year, the Senate has voted to confirm Supreme Court Justice Neil Gorsuch and 10 circuit court nominees - the most of any president in his first year since Richard Nixon.
Sen. Dianne Feinstein, the top Democrat on the Judiciary committee, said in a statement Tuesday that Talley and Mateer "should not be federal judges" and urged Grassley to slow down the process.