Trump's election and the initiatives he has undertaken since the January 20 inaugural, most dramatically on the refugee travel ban, foreshadow years of new controversies to be resolved by the nation's federal judges.
That will put the Supreme Court, and potentially this new jurist, at the fulcrum of Trump's efforts to change life in America.
In addition, the nearly year-long Republican stall of Democratic President Barack Obama's nominee for the Scalia seat has increased the political stakes. This Senate confirmation process begins with partisan payback in the air.
That is on top of what was evident last February when Scalia died suddenly at a remote Texas hunting resort: The Supreme Court is deeply divided and every vote matters. A single justice among the nine can tip the balance on civil rights, criminal law and corporate regulation.
Rarely has there been a moment in American history of such widespread national discord, internal court divisions, and the opportunity for a new tie-breaking justice.
CNN's Jeff Zeleny reported Tuesday that the two leading candidates are believed to be Neil Gorsuch
, who sits on the Tenth Circuit Court of Appeals in Denver, and Thomas Hardiman
, who sits on the Third Circuit Court of Appeals in Pittsburgh. Both have met with Trump.
The jurist who eventually secures the lifetime post will likely decide the law not just for this generation but for the next.
Scalia, who died a month short of his 80th birthday, served for three decades, and given the relatively youthfulness of the finalists for tonight's announcement, a new justice could sit on the bench for 30 years as well.
The nation's judiciary serves as a check on the legislative and executive branches. Not even two weeks as president, Trump has spurred a raft of controversy and litigation, particularly to his order last Friday
temporarily barring refugees and certain other foreigners from entering the country.
Most divisive is the part blocking entry for people from seven Muslim-majority countries even if their visas were valid.
Over his eight years as president, Barack Obama undertook numerous initiatives that were challenged in federal courts, including on immigration, health care and environmental regulation.
But none of his moves prompted such instant litigation and protest, which played out with demonstrations at the nation's airports and in public squares over the weekend. Lower court judges have temporarily suspended parts of the order.
Trump, who has expressed pride in his disruptive ways, has asserted that the refugee restrictions would improve national security and protect the country from terrorists. Congressional leaders from both parties, along with immigration experts and legal analysts, have condemned the policy. Many say it is counterproductive to security interests and unlawful.
The ultimate arbiter of the constitutionality of Trump's sweeping new moves would be the Supreme Court.
A Polarized Court
On the current bench sit four Republican appointees who generally vote conservative (Chief Justice John Roberts and Justices Anthony Kennedy, Clarence Thomas and Samuel Alito) and four Democratic appointees who regularly vote liberal (Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan).
Scalia was a reliable right-wing vote, which made the court one of the most conservative in modern times. With Scalia, it curtailed the protections of the 1965 Voting Rights Act and other racial remedies for discrimination; allowed more prayer in public places; and restricted class-action lawsuits brought by aggrieved workers and consumers against big corporations.
Yet, because of Kennedy's centrist tendencies, conservatives were unable to roll back significantly abortion rights, as established by the 1973 Roe v. Wade decision, or race-based policies intended to enhance student diversity at universities, as allowed under the 1978 Regents of the University of California v. Bakke.
Kennedy, who cast the deciding votes to affirm abortion rights and campus affirmative action in 2016, was also the crucial fifth vote to declare a constitutional right to same-sex marriage in 2015
He remains on the bench, but he is 80 years old and has indicated to some close friends and associates an interest in retiring. If he were to step down in the near future, and Trump made successive nominations, he could transform the court and the law in America.
Trump has said he is looking for justices who would reverse Roe v. Wade, which made abortion legal nationwide. He has said he wants states to have the power to determine when a woman has the right to end a pregnancy.
Other retirements are possible. Ginsburg, who will turn 84 in March, is the court's eldest justice. Breyer will turn 79 in August.
Recalling Merrick Garland
Senate Democrats and their liberal allies anticipate such near-term potential for change. With Republicans still holding the majority in the chamber, 52-48, Democrats know it would be difficult to derail Trump's choice.
But they appear prepared to make the confirmation process as rocky as possible to dissuade Trump from an especially conservative choice if a more consequential vacancy arises, for example, with a Kennedy retirement.
Democrats have tried to focus public attention on the Republican Senate majority's 10-month refusal to act on Obama's March 16 nomination of Merrick Garland
, a former prosecutor who is chief judge of the US Court of Appeals for the District of Columbia Circuit.
Sen. Amy Klobuchar, a Minnesota Democrat who serves on the Senate Judiciary Committee, has suggested she would support a filibuster of Trump's nominee. That would require 60 votes to cut off debate, rather than a simple majority for approval.
It's unclear how real the threat of a filibuster may be. Democrats privately discussed their tactics during a closed-door retreat in West Virginia last week, CNN's Manu Raju reported
, and some in the party tried to persuade liberal firebrands to let Republicans confirm Trump's pick -- citing fears the GOP might gut the rules regarding the filibuster in retaliation for blocking the nominee.
Responding to Democratic filibuster warnings, Republican Sen. Bob Corker, of Tennessee quipped, "I've never heard of people filibustering someone before they know who it is. I mean it could be Merrick Garland."