Washington, D.C. ? The Senate’s revived legislation to legalize millions of unlawful immigrants faces a critical test Thursday after surviving potentially fatal challenges.

Attempts from the right and left to alter key elements of the delicate bipartisan compromise failed Wednesday, including a Republican proposal to deny illegal immigrants a path to citizenship and Democratic bids to reunite legal immigrants with family members.

The Senate killed, by a 56-41 vote, an amendment by Sen. Christopher Dodd, D-Conn., to provide more green cards for parents of U.S. citizens. By a 55-40 margin, it tabled a proposal by Sen. Robert Menendez, D-N.J., to give family members of citizens and legal permanent residents more credit toward green cards in a new merit-based points system.

A make-or-break procedural vote was set for Thursday, however. Facing determined opposition from conservatives who call the bill amnesty, leaders need 60 votes to keep the measure alive and complete it as early as Friday.