Senate Republicans and conservative activists on Friday immediately called on the White House to nominate a moderate jurist to replace retiring Supreme Court Justice John Paul Stevens, and urged President Barack Obama to tap a replacement who will decide cases impartially.

The 89-year-old Stevens is widely considered to be the leader of the court’s liberal flank, and many Democrats hope President Barack Obama replaces him with a like-minded jurist.

But GOP Senators, while thanking Stevens for his more than three decades of service, made clear Friday that an ideological nominee will face a tough road toward confirmation.

“Justice Stevens devoted his career to our nation’s judicial system, participating in some of the most important cases in our history. While he and I may have different judicial philosophies, I thank Justice Stevens for his service, and I wish him well in his retirement,” said National Republican Senatorial Committee Chairman John Cornyn (Texas), who also serves on the Judiciary Committee.

“Our nation deserves a Supreme Court nominee who is committed to deciding cases impartially based on the law, not on personal politics, preferences or what’s in the nominee’s heart. It is my expectation that Senators on both sides of the aisle will work to ensure both a dignified and respectful process for our next nominee,” he added.

Likewise, Minority Leader Mitch McConnell (R-Ky.) thanked Stevens for his service but warned that his Conference will make a “vigorous case” for a moderate replacement.

“Even if Justice Stevens’ liberalism has led to many decisions I oppose, I respect his devotion to the institution and the gentlemanly manner in which he always carried out his work. I wish Justice Stevens and his wife Maryan all the best in their future endeavors,” McConnell said in a statement, adding that, “As we await the President’s nominee to replace Justice Stevens at the end of his term, Americans can expect Senate Republicans to make a sustained and vigorous case for judicial restraint and the fundamental importance of an even-handed reading of the law.”

Conservative activists, however, were more blunt in their warnings for the Obama administration.

Carrie Severino, chief counsel and policy director for the Judicial Crisis Network, accused Obama of pursuing a “left-wing agenda,” and warned the White House against using its Supreme Court picks to further its liberal goals.

“The American people are fed up with President Obama’s left-wing agenda and will make their frustration known at the polls. But he still has one ace up his sleeve: packing the Supreme Court with rubber stamps instead of judges. To an activist judge, the constitution represents an inconvenient truth that they will distort, ignore, or defy to push their radical liberal agenda,” Severino said in a statement.

Senate Democrats, for their part, praised Stevens for his service and called for a smooth confirmation process for his successor.

“Justice Stevens’ unique and enduring perspective is irreplaceable; his stalwart adherence to the rule of law is unparalleled. The federal judiciary, and indeed the entire nation, will miss his principled jurisprudence. While it is with a heavy heart, I wish him the best in his retirement,” Judiciary Chairman Patrick Leahy (D-Vt.) said in a statement, adding that, “I hope that Senators on both sides of the aisle will make this process a thoughtful and civil discourse. … All Senators should strive to fulfill their constitutional duty of advise and consent, and give fair and thorough consideration to Justice Stevens’ successor.”

Similarly, Majority Leader Harry Reid (D-Nev.) called Stevens a “strong presence on the court” and called on Republicans to work with Democrats to swiftly confirm a new justice.

“I am confident that President Obama will use the same wisdom that he showed with his nomination of Justice [Sonia] Sotomayor and name a well-qualified successor. I encourage my Republican colleagues to join us in conducting fair, respectful hearings and swift confirmation of the President’s nominee,” Reid said in a statement.