President Trump will nominate his second justice to the Supreme Court in two years Monday, and that pick could further shift the court to the right and solidify its conservative bent for years or even decades.

“We have to pick a great one,” Trump said during campaign rally in North Dakota. “We have to pick one that’s going to be there for 40 years, 45 years … We need intellect. We need so many things.”

If confirmed by the Senate, the nominee would replace retiring Justice Anthony Kennedy. Throughout his three decades on the court, Kennedy was often the decisive vote in close cases, particularly those involving abortion rights.

With the potential for abortion and other key issues to come before the court — and the new justice as a critical vote — Senate Democrats have started gearing up in opposition even before Trump’s announcement, saying his finalists tended to favor corporations over people and are hostile to abortion rights and other matters of privacy.

Some opponents stressed that Trump worked off a list compiled by members of conservative legal organizations, particularly the Federalist Society and the Heritage Foundation.

Conservatives, who were thrilled when Trump nominated Neil Gorsuch last year, are mobilizing campaigns in support. White House aides said they have prepared “rollout packages.”

The Republicans have a 51-49 advantage in the Senate, but one key member, Sen. John McCain of Arizona, is ill and may not be able to participate in the confirmation process.

Abortion

The president made it clear in October 2016 that he would overturn Roe vs Wade, the 1973 Supreme Court decision that legalized abortion nationwide, because he would only appoint “pro-life” judges.

“Roe v. Wade could be over turned or at least abortion could be rolled back,” said  University of Richmond law Professor Carl Tobias. “That’s a position I think many conservatives would agree with.”

With a conservative appointee, many women would result in “unsafe illegal abortions,” according to Elizabeth Wydra, president of the Constitutional Accountability Center, a non-partisan law firm in Washington.

LGBT rights

According to Wydra, Kennedy supported LGBT rights, but there are concerns that the 2015 case that legalized marriage equality could be reexamined. The court may also be asked to rule on the Trump administration’s decision not to defend Title VII protections for gay and lesbian couples. Adoption, custody and divorce could also have limitations on marriage equality ruling.

Election issues

Questions about campaign finance and spending by donors who don’t reveal their identities may return to the court. The 2010 Citizens United decision, which allowed corporations to donate money, is the most recent and controversial example.

Trump would like to have another justice who believes corporations should be able to donate as much as they want, Tobias said.

Kennedy voted in favor of making it harder for people to vote, Wydra said, so another pick that reinforced that view could push the court more to the right.

Guns

The court has avoided gun issues for a few years mostly because neither party knew which side Kennedy would take. Trump wants someone that will have a broad view of the Second Amendment, Tobias said.

“The president has had strong support from the NRA he would favor very strong gun rights and the Second Amendment…. it would be harder to impose more stricter regulation,” said Tobias. “A new justice could strike down for example regulations four other justices felt were too restrictive.”

Immigration

The court is expected to soon see cases on the Deferred Action for Childhood Arrivals program and the ability of local governments to act as sanctuary cities.

One of Kennedy’s final rulings was to support Trump’s right to limit travel to the United States for people from certain countries the government designates.

Also likely to reach the court in the next few years is the zero tolerance policy for asylum seekers and other potential immigrants, which has resulted in families being separated by the government.

One issue that could be important would be challenges of family separations, said Tobias. “We want to make sure the next justice follows the law and the facts and doesn’t feel obliged to follow the preferences of the president who put him or her on the bench.”