The retirement on July 31 of US Supreme Court Justice Anthony Kennedy has stunned liberals - and conservatives are salivating at the prospect of a decisively conservative Supreme Court bench for decades to come.
And it has raised the stakes even higher in mid-term congressional elections in November, when 33 of the Senate's 100 seats will be up for re-election.
The nine Supreme Court judges are appointed for life. President Donald Trump last year appointed conservative Neil Gorsuch to one seat on the bench. The retirement of Justice Kennedy opens up another seat for a conservative appointment, the implications of which could potentially reshape American society.
Only the Senate can stall the nomination of a replacement for Justice Kennedy. Republicans currently control the Senate with 51 seats, while Democrats have 49 - including two independents.
"Justice Kennedy's retirement makes the issue of Senate control one of the vital issues of our time; the most important thing we can do," President Trump told a wildly cheering crowd in Fargo, North Dakota, on Wednesday night.
Justice Kennedy was largely conservative, but occasionally sided with the liberal wing of the court - for instance in a 2015 ruling legalising same-sex marriage.
That, and the landmark 1973 Roe v Wade case which legalised abortion, may be revisited when the nine-person bench, already conservative-leaning with the appointment of Justice Gorsuch, becomes more firmly conservative.
The retirement of Justice Kennedy opens up another seat for a conservative appointment, the implications of which could potentially reshape American society.
The Republican Party will try and rush through an appointment and confirmation for a new justice before the mid-term elections. "We have to pick one that's there for 40 years, 45 years," Mr Trump told his supporters in Fargo.
Mr Joshua Matz, publisher of the Take Care legal blog, wrote in the Washington Post: "Keen to reshape American life on a startling scope and scale, conservatives will race to confirm a reliable vote.
"Things will get ugly - very ugly. Roe v Wade hangs in the balance. So do many other famous precedents," added Mr Matz, who was a law clerk to Justice Kennedy from 2014 to 2015.
Abortion rights group Planned Parenthood Federation said: "The significance of... (the) news cannot be overstated: The right to access abortion in this country is on the line."
President Trump has said the issue of same-sex marriage is settled, but activists fear the notoriously mercurial President will change his mind under the influence of arch conservatives. "I don't think 'devastated' is too strong a word," Mr James Obergefell, author and plaintiff in the 2015 case, told CNN.
Democrats and liberal groups have said they will fight tooth and nail to stall the nomination and confirmation of a replacement justice.
Democrats hope to replicate the play of Republican Majority Leader Mitch McConnell, who had held up an appointee by former president Barack Obama to the bench on grounds that it was too close to the November 2016 presidential election - thus sealing the fate of the seat given to Mr Gorsuch after Mr Trump won that election.
The seat to be vacated by Justice Kennedy is even more important, Democratic Party Senator Kamala Harris told MSNBC on Wednesday.
"Gorsuch was about one conservative replacing another conservative. This is about a swing vote," she said. "Everything lies in the balance in terms of how this court could swing on everything from... Roe versus Wade, to what we did in terms of same-sex marriage, to so many issues that are about fundamental rights." She added: "We have to fight to push it off. The decision that we make is going to have a generational impact."
Analysts expect the base for both parties to be re-energised, pointing to a high turnout for the mid-term elections. Still, the chances of the Democrats delaying the confirmation of a new justice, or in flipping the Senate so that they can further delay the appointment until the next presidential election in November 2020, are seen as slim.
The party has no leverage, said Dr Glenn Altschuler, professor of American Studies at Cornell University. "Kennedy's successor will be on the bench long before the elections of 2018," he said.