Recent research I conducted with Tom S. Clark and B. Pablo Montagnes of Emory University found that Supreme Court justices’ ideological leanings intensify greatly with close votes. When a ruling comes down to a 5-4 split, justices in the majority are more apt to decide according to their personal affinities, since any change in their votes would alter the outcome of the case. Furthermore, when a case has a high media profile, the influence of ideology is even stronger.

The result is sometimes termed “politics from the bench.” When a ruling matters greatly because it sets legal precedent, our research shows that “justices tend to polarize rather than moderate.” Moreover, at the Supreme Court, justices have discretion over which cases they hear, allowing them to strategically step in and clarify areas of the law they feel are ambiguous or incomplete. Almost by definition, that means these cases often create room for discretion because of unclear language in the Constitution or because the drafters did not foresee certain issues.

It is no surprise that the Supreme Court is hardly an apolitical institution. Political ideology, along with justices’ lifelong tenure, often makes high-court nominations a battleground between Democrats and Republicans. After all, the political makeup of the court can have an impact for decades to come.

What is eye-opening, though, is that a justice’s political ideology, whether liberal or conservative, weighs even more heavily in close cases—exactly when it matters the most. This makes Kavanaugh’s appointment to the court all the more politically sensitive. If approved, he would replace retiring Justice Anthony Kennedy, who often served as the “swing vote” on the Supreme Court, balancing liberal and conservative ideologies.

With Kavanaugh, a political conservative, on the court, the impact could be felt with cases involving such high-profile issues as abortion, affirmative action, and LGTBQ rights. Kavanaugh has reportedly referred to Roe v. Wade, which legalized abortion 1973, as settled law; however, that may not indicate how the nominee would decide on related cases in the future, particularly when it comes down to a close vote.

When the law is viewed as being clear, justices do tend to decide according to the accepted constitutional interpretation. Further, when there is a clear majority of opinion, justices may take more of a centrist view or even cross “party lines” in their voting. But when the Constitution is ambiguous and the legal stakes are high, our research shows that a justice’s own political views tend to take over.

This reality was illustrated in a scathing dissent written by Justice Elena Kagan in the recent case of Janus v. American Federation of State, County and Municipal Employees, which was decided in a 5-4 vote and struck a big blow to public sector unions. Writing for the majority, Justice Samuel Alito argued that requiring nonunion members to contribute “agency fees” to cover the cost of collective bargaining violated their First Amendment rights. Kagan, however, referred to her conservative colleagues in the majority as “black-robed rulers overriding citizens’ choices.” Because the case was so close and important—upsetting a 40-year-old precedent—Kagan implied that the conservative justices’ ideologies dictated their votes.

Kavanaugh’s Senate confirmation hearings, which are expected to last three or four days, were set with the goal of seating a new justice by the time the next Supreme Court term begins in early October. If Kavanaugh is confirmed, political and legal eyes will be on this new justice for his votes and opinions. If our research is any indication, then the full extent of his ideology and its influence will only be revealed over time as high-profile cases split the liberals and conservatives on the court.

Jörg L. Spenkuch is a professor at the Kellogg School of Management at Northwestern University.