Per The Hill, McConnell said his opposition is not based on "race or gender," but on concerns about Jackson's judicial philosophy and her record, which critics have characterized as being soft on crime.
Despite McConnell's vote whipping, it is unlikely Republicans will be able to block Jackson's confirmation. Even if all 50 Republican senators vote against Jackson, Vice President Kamala Harris can still break the tie in the nominee's favor.
Sen. Joe Manchin (D-W.Va.), who has broken ranks with his fellow Democrats in the past, said last week that Jackson can count on his vote. Sen. Susan Collins (R-Maine) said the same on Wednesday, suggesting that Harris' intervention will not be necessary.
According to The Hill, Sen. Mitt Romney (R-Utah) said he has not yet decided which way he will vote.