Following Supreme Court Justice Antonin Scalia's death, Republicans are arguing that President Barack Obama should not appoint someone to the Supreme Court during an election year — largely out of fear that Obama will use his last year in office to appoint a liberal judge to replace the conservative Scalia.

But Obama said he's moving forward with a nominee anyway. And it turns out that nominating a justice during an election year is not totally unprecedented, as this chart by graphics designer David Mendoza shows:

Mendoza explained that the norm in the past several decades was to avoid nominating someone to the Court in the six months before a presidential election, so nominating a replacement for Scalia would fall within recent norms. Mendoza wrote:

In June 1968, President Lyndon Johnson nominated two people to the Supreme Court. Even though the Senate was controlled by members of the president’s party, Southern Democrats and conservative Republicans like Strom Thurmond stopped both those nominees from being confirmed. Johnson withdrew both nominations just a month before the election of 1968. Since then, there has been an informal and vague rule known as the Thurmond Rule that states no judicial nominee would be considered that close to a presidential election. However, senators dispute exactly when the Thurmond Rule goes into effect or how strictly it should be followed. Generally, six months before a presidential election is considered the standard. This would mean that the current vacancy on the court falls outside this time frame.

Of course, norms can change. American politics have become more polarized during Obama's time in office, so Supreme Court nominations are more contentious.

There's also one caveat to Mendoza's chart: It includes a broader definition of election year. Some people use the term election year to mean the year of an election — so 2016 is an election year, but not any period in 2015. Others may use the term to mean the year preceding an election — so November 2015 to November 2016.

In Mendoza's chart, the nominees dated after John Paul Stevens meet the narrower definition of election year.

By the narrower standard, Justice Anthony Kennedy's nomination — the most recent on the chart above — might not count as an election year nomination, especially in the broader context of the political battles of the time. Vox's Timothy Lee explained:

Here, conservatives will have a strong retort: Not only was Anthony Kennedy nominated in 1987 — not 1988 — but the only reason he was nominated at all was because Democrats had rejected the nomination of Robert Bork a year earlier. All told, President Reagan had more than 18 months to fill the vacancy created by Justice Lewis Powell's retirement, compared with about 11 months for Obama.

Suffice it to say, then, there are enough complicating factors in this debate that no one chart will settle it. But it does provide some interesting context.

VIDEO: President Obama on the passing of Justice Scalia