As he serves out his last months in office, President Barack Obama will nominate a Supreme Court justice in the Rose Garden at 11 a.m. and is again calling on members of the U.S. Senate to "do their jobs" and take up his candidate.

The White House has been vetting candidates since the death of Justice Antonin Scalia, which created a vacancy on a court that is frequently divided in its rulings.

Senate Republicans have pledged not to consider Obama's nominee in a move designed to let this year's elections run their course and enable the next president make the nomination.

"The death of Justice Scalia represents a significant loss for our country and while finding the right person to take the seat he occupied will clearly be a monumental task, the American people? should have a voice in the selection of the next Supreme Court Justice and the vacancy should not be filled until we have a new President," Senate Majority Leader Mitch McConnell said in late February.

At the time, McConnell told reporters at the US Capitol: "The Judiciary Committee has unanimously recommended that there be no hearings, I agree with that, and number two, this nomination will be filled by the next president elected in November."

Obama and others say the Senate is constitutionally bound to consider presidential nominees to the high court.

"I'm confident you'll share my conviction that this American is not only eminently qualified to be a Supreme Court Justice, but deserves a fair hearing, and an up-or-down vote," Obama wrote in a letter released Wednesday morning. "In putting forward a nominee today, I am fulfilling my constitutional duty. I'm doing my job. I hope that our Senators will do their jobs, and move quickly to consider my nominee. That is what the Constitution dictates, and that's what the American people expect and deserve from their leaders."

Obama said that prior to making his pick, he had "consulted with legal experts and people across the political spectrum, both inside and outside government" and reached out to every member of the Senate.

Obama wrote that he's focused on ensuring his nominee meets three principles.

The president wrote:

"First, a Justice should possess an independent mind, unimpeachable credentials, and an unquestionable mastery of law. There is no doubt this person will face complex legal questions, so it is imperative that he or she possess a rigorous intellect that will help provide clear answers.

Second, a Justice should recognize the limits of the judiciary's role. With a commitment to impartial justice rather than any particular ideology, the next Supreme Court Justice will understand that the job is to interpret the law, not make law.

However, I know there will be cases before the Supreme Court in which the law is not clear. In those cases, a Justice's analysis will necessarily be shaped by his or her own perspective, ethics, and judgment.

Therefore, the third quality I looked for in a judge is a keen understanding that justice is not about abstract legal theory, nor some footnote in a dusty casebook. It's the kind of life experience earned outside the classroom and the courtroom; experience that suggests he or she views the law not only as an intellectual exercise, but also grasps the way it affects the daily reality of people's lives in a big, complicated democracy, and in rapidly-changing times. In my view, that's an essential element for arriving at just decisions and fair outcomes."