Trump's court pick could give him decades of influence, but other presidents have had more

After days of testimony before the Senate, Neil Gorsuch could soon face a confirmation vote for the ninth seat on the Supreme Court. If confirmed, he'll likely be there for a while.

By nominating Gorsuch, President Donald Trump is giving himself decades of influence on the judicial branch, according to a CNBC analysis. A 49-year-old judge would give Trump up to 30 years of influence on the bench. That's far higher on a years-per-justice basis than many presidents.

But unless he manages to get re-elected in 2020, and appoint more justices, Trump is likely to end up in the bottom half of presidents, based on the total tenure of their appointed justices. Some presidents have secured more than a century of influence on the court.

The judicial branch is unique in that Supreme Court justices are appointed for life or until retirement. That means a president's policies — or at least the legal viewpoints of those they nominate to the court — can live on far beyond their time in the Oval Office. President Franklin Roosevelt, for example, sent nine justices to the court during his 12 years in office.

All told, those justices served for 148.7 years and decided some of the most important cases in American history. By adding up the years served of all the justices appointed by a president, we can get a sense of the total influence that president has had on the history of the court. Trump's single seat may last longer, but some presidents have shaped the court more.

Using actuarial tables from the Social Security Administration, we're able to get a sense of how long each sitting justice will remain on the court.

Think of life expectancy, but for any given age. A female's life expectancy at birth may be 81, but when she's made it to her mid-60s, she can expect to live past 86. It should be noted that these are estimates: Any given justice could live longer than projected, or not make it their full projected lifetime. We're also projecting to the justices' end of life; there's no way to know if some justices will chose to step down before then.

By that measure, Justices Elena Kagan and Sonia Sotomayor are expected to remain on the bench the longest out of the current court. Both were appointed by former President Obama. If they stay through their life expectancies, that will give Obama more than 50 years of influence on the court. With Gorsuch's projected 30 years on the bench, Trump would have two decades less of judicial influence.

Presidents' placements on the Supreme Court matter because studies have shown that justices are prone to voting along the same ideological lines as the party that nominated them. Not only do they tend to toe the party line, but they are also more likely to agree with the president who appointed them than with subsequent presidents, even if those later presidents are from the same party. That's what academics call the "loyalty effect."

Of course, most justices aren't as politically driven as the presidents who place them on the bench, and some actually turn out to decide cases contrary to their benefactor's political leaning. Justices Anthony Kennedy and Sandra Day O'Connor turned out to be far more middle of the road than the president who appointed them, Ronald Reagan. Justice David Souter, nominated by George H.W. Bush in 1990, became far more liberal during his years on the court.

Still, Republican-nominated justices have dominated the court through much of its history.

That's certainly been true in the past 50 years: After Roosevelt's all-Democrat-appointed court, Republicans gained ground after the 1960s with a string of 11 justices nominated by presidents Nixon, Ford, Reagan and Bush.

President Jimmy Carter, who fell in the middle of that string of Republicans, didn't get to pick an appointee. Had Obama managed to get a third nominee through the Senate following Justice Antonin Scalia's death in 2016, that cumulative gap may have closed, but instead the court remains heavy with Republican nominees.

Analyses put Gorsuch on the conservative end of the spectrum near Samuel Alito, but justices of all stripes tend to drift to the left the longer they stay on the court. That could help explain why, despite the influence of Republican appointees, the court has generally stayed balanced or even become more ideologically liberal over time. Time will tell the extent to which Trump's choice will shape the court for years to come.