WASHINGTON - A Senate showdown over a popular anti-human trafficking bill escalated Tuesday, as Democrats filibustered the measure in protest of Republican-backed abortion restrictions.

The heated standoff jeopardizes not only passage of the otherwise bipartisan bill to fight human sex trafficking but also leaves Senate confirmation of President Obama's choice for attorney general in limbo.

Senate Majority Leader Mitch McConnell (R., Ky.) has refused to consider the confirmation of Loretta Lynch, who would become the first African American woman to lead the Department of Justice, until the Senate dispatches with the human trafficking bill.

But Senate Democrats refused to advance the human trafficking measure until Republicans strip out a provision that would restrict money from a new $30 million victims fund from being used for abortion services except in rare cases. Republicans refused.

The Senate voted, 55-43, failing to reach the 60-vote threshold needed to advance the bill. A second vote also failed.

Civil rights and African American leaders have joined the White House in criticizing Senate Republicans for delaying Lynch's confirmation. She has faced unusually strong opposition from GOP senators despite her professional qualifications as the U.S. attorney for New York's Brooklyn office.

But McConnell said Tuesday that Democrats were to blame for the holdup, as they cater to "left-wing" abortion-rights groups.

"Democrats filibustering help for terrified children and abused women would represent a new low here in the Senate," McConnell said shortly before the vote.

Democrats, though, said Republicans should simply remove the abortion restrictions to allow the bill to advance.

Democrats have argued that even though Congress has a long-standing agreement to prohibit using taxpayer funds for abortion except in cases of rape, incest or a threat to the life of the mother, adding the restriction to the trafficking bill's victims fund is an unacceptable expansion.