The announcement of President Trump's Supreme Court nominee will unleash a blizzard of commentary, advertising and social media campaigns aimed at influencing senators and the public. But to win the real battle for the future of the high court, the nomination and the messaging around it should be aimed at the one man who truly matters: Anthony Kennedy.

For while there will — and should — be a fierce debate over the nomination, the outcome of the fight to replace Justice Antonin Scalia will probably not change the court's balance of power. What could change the balance — dramatically — is if Trump gets to pick another justice, particularly if that vacancy is created by the departure of one of the court's three oldest members: Justices Ruth Bader Ginsburg, Stephen Breyer and Kennedy. And since it is very unlikely that Ginsburg or Breyer would voluntarily retire during this presidency, the question of whether a court-shifting pick is willingly handed to Trump rests with Kennedy.

The justice I clerked for — Byron White — was inclined to retire as soon as a Democratic president took office. Although White was ideologically distant from the Democratic Party, he felt that because a Democrat (John F. Kennedy) had selected him, a Democrat should name his replacement. When, after 12 years of Republican control of the White House, Bill Clinton became president in 1993, White retired just 60 days after the inauguration. Might Anthony Kennedy — appointed by President Ronald Reagan — feel the same obligation today to a new Republican president?

No one but Kennedy and those closest to him know for sure. But the battle over the current court vacancy could influence Kennedy's decision, especially because Kennedy owes his seat on the court to a Supreme Court confirmation battle of a generation ago: the Senate's rejection of the nomination of Robert Bork in 1987. Thus, Trump, Senate Republicans and Senate Democrats would be smart to keep Kennedy in mind as they consider the upcoming nomination and how to respond.

If Trump picks one of the two most widely speculated choices — federal appeals court judges William Pryor or Neil Gorsuch — that will likely encourage Kennedy to stay in place. While Kennedy is said to have some personal affinity for Gorsuch (one of his former law clerks), both Pryor and Gorsuch reject Kennedy's most important views on constitutional principles — particularly his dedication to a core concept of the "dignity of free persons." Kennedy's dignity principle is an idea he articulated in his Senate confirmation hearing nearly 30 years ago and has been central to many of his opinions in the years since, particularly in cases upholding abortion rights and LGBT rights.

What's more, a highly conservative first pick by Trump would offer an inauspicious signal for what might come next. The last three Republican presidents have all started with more moderate selections (Sandra Day O'Connor for Reagan, David Souter for President George H.W. Bush and John Roberts for President George W. Bush) and then moved to the right with their second picks (Scalia, Clarence Thomas and Samuel Alito, respectively). If Trump begins with a far-right conservative such as Pryor or Gorsuch, what might his second nominee look like? Definitely not like Kennedy.

For Senate Republicans, keeping the prospect of a Kennedy resignation in mind would counsel resisting the temptation to end the right to filibuster Supreme Court nominations. Eliminating any power of the minority to stop the most extreme possible nominee would probably be a red flag to Kennedy — an indication that the way was clear for a balance-shifting nominee who rejected Kennedy's views and moved the court in a radical new direction.

Senate Democrats, too, must be mindful of how their approach to the nomination could affect Kennedy's thinking. While it is tempting to begin the confirmation process with an intent to avenge the injustice done to President Barack Obama and his nominee, Judge Merrick Garland — and no one could be more tempted than I am — this urge must be resisted. An attitude of score-settling and partisan bitterness would likely be off-putting to Kennedy.

Rather, even as they resist a nominee as extreme as Pryor or Gorsuch, Democrats should make clear that they would accept a more moderate candidate — much as Democrats did a generation ago when Reagan pivoted from Bork to Kennedy. They should make clear not only what they are against in a Supreme Court nominee, but also what they are looking for in a Trump selection. And they should emphasize that they are dedicated to a concept of "dignity of free persons," along the lines of Kennedy's jurisprudence, and will not accept a nominee who would reverse the progress such a philosophy has achieved.

Thus, even as this nomination battle unfolds, all players should keep an eye on the even more significant fight that could lie ahead — and the man who will decide whether it comes or not.

Ronald Klain was chief counsel for the Senate Judiciary Committee during the David Souter and Clarence Thomas nominations, an associate counsel to President Bill Clinton for the Ruth Bader Ginsburg and Stephen Breyer nominations, and an assistant to President Barack Obama advising on the Sonia Sotomayor and Elena Kagan nominations. He wrote this article for the Washington Post.