WASHINGTON — If there were any doubt, Senator Harry Reid clearly has one last, good fight in him.

Instead of cruising to retirement after securing a two-year budget deal last fall and essentially bequeathing his leader’s suite to Senator Chuck Schumer of New York, Mr. Reid, Democrat of Nevada, is waging war with Republicans over the Supreme Court vacancy left by the death of Justice Antonin Scalia.

Though the battle is decidedly uphill, it is one that supporters of Mr. Reid, 76 and in his 30th and last year in the Senate, say he is well suited to wage. Win or lose, it will be a fitting capstone to a career that included eight years as majority leader, and countless bitter feuds, during one of the most rankly partisan periods in Senate history.

“It’s tailor-made for him,” said Senator Tim Kaine, Democrat of Virginia, who was with Mr. Reid in Las Vegas days after Mr. Scalia’s death. Mr. Kaine said that Mr. Reid viewed the Republicans’ refusal to even meet with a potential Supreme Court nominee as disrespectful to President Obama and a threat to the Senate as an institution.

“It’s a battle for the job description of what a U.S. senator is,” Mr. Kaine said. “We should be guardians of this institution. To have a battle in your last year, to try to guard something important about the institution, that’s a good battle for Harry Reid to have.”