President Barack Obama on Wednesday nominated appeals court judge Merrick Garland to the Supreme Court, and in the process challenged the Republican-led Senate to begin the confirmation process immediately. However, Republicans have adamantly refused to consider Obama’s choice to fill the open seat after the untimely death last month of Associate Justice Antonin Scalia.

In a Rose Garden press conference, Obama hailed Garland as “one of America’s sharpest legal minds” in highlighting his work leading the investigation into the Oklahoma City bombing and the subsequent prosecution and conviction of Timothy McViegh.

Garland, 63, is the chief judge for the United States Court of Appeals for the District of Columbia, a court whose influence over federal policy and natural security matters has made it a reported proving-ground for potential Supreme Court appointees.

If confirmed, Garland would be expected to align with the more liberal members of the Supreme Court, yet court observers say he is not specifically a “down the line” liberal. On matters of criminal defense, Garland has earned a reputation as a centrist, and one of the few Democratic-appointed judges whom Republicans might have fast-tracked to confirmation. Circumstances on Capitol Hill are vastly different from when Garland was nominated to the D.C. Circuit in 1995. Even then he had to wait 2 1/2 years to win confirmation to the Appeals Court. Then, as now, one of his main opponents was Sen. Chuck Grassley of Iowa, who is the current head of the Senate Judiciary Committee. The Republican-controlled Senate has vowed not to hold hearings for any nominee, with leaders saying they want to leave the choice to the next president, thereby denying Obama the chance to alter the ideological balance of the bench before he leaves office next January.

Obama’s selection of Garland has reportedly deflated some of the energy among the Democratic base. Many progressives and civil rights activists wanted an African American to be nominated to expand the court’s diversity. If confirmed, Garland would be the oldest Supreme Court nominee since Lewis Powell, who was 64 when he was confirmed during the Nixon Administration in 1971.

After the nomination, Republicans immediately set up a task force that will orchestrate attack ads, petitions and media outreach to scuttle Garland’s chances of gaining a hearing. Obama allies are scheduled to run a Democratic effort to support Garland in targeting states where Republicans might feel political heat for opposing hearings.

American voters are divided along party lines as to whether the Senate should vote this year on a nominee. The results of an NBC News/Wall Street Journal poll last month found 43 percent of respondents saying “yes” to a Senate vote, versus 42 percent who prefer to leave the position vacant and to wait for a nomination by a new president. Fifteen percent had no opinion. Among Democratic voters, 81 percent want the Senate to vote this year, with only 9 percent disagreeing. The numbers are flipped almost exactly among Republican respondents with 81 percent preferring the position remain vacant, and 11 percent opting for a Senate vote. A CBS News poll revealed similar responses: More than four in five Republicans believe the Supreme Court vacancy should be filled by the next president and as many Democrats (77 percent) think President Obama should select Scalia successor. The political landscape on both sides isn’t budging: 47 percent of respondents to the CBS News poll said the president should nominate someone now, while 46 percent declare he should not.