President Donald Trump threw his support Wednesday behind legislation that looks to curb the level of legal immigration into the United States by proposing a skills-based immigration system.

Trump backed the effort from Republican Sens. David Perdue and Tom Cotton in a speech at the White House. But the plan faces long odds in Congress, where both Democrats and Republicans have responded to the proposal with skepticism.

The proposals also get into an already crowded line of measures that Congress is considering, including health care, tax reform, a budget and raising the debt ceiling, making it unlikely that the plan will get passed any time soon.

Top White House aides have been working with Perdue and Cotton on the bill that — if passed — would dramatically remake the current immigration system, which allows a number of ways to bring family members to the US along with job-based visas.

Trump cast the proposal as a way to protect American workers by reducing unskilled immigration and creating a merit-based system that grades possible immigrants based on their ability to work in the United States.

“It has not been fair to our people, to our citizens, to our workers,” Trump said of the current immigration system, specifically citing low-income and minority workers.

The bill, Trump said, “would represent the most significant reform to our immigration system in half a century.”

Long odds in Congress

Stephen Miller, Trump’s top policy aide who has long advocated for changes to the immigration system and had a key hand in crafting this legislation, cast the measure as “the largest proposed reform to our immigration policy in half a century.”

“This is what President Trump campaigned on. He talked about it throughout the campaign, throughout the transition, and since coming into office,” Miller said Wednesday afternoon. “This is a major promise to the American people to push for merit-based immigration reform that protects US workers, protects US taxpayers, and protects the US economy, and that prioritizes the needs of our own citizens, our own residents and our own workers.”

Arguing this plan would make the immigration fairer, Miller continued, “It’s pro-American immigration reform that the American people want, that the American people deserve, and that puts the needs of the working class ahead of the investor class.”

Cotton, of Arkansas, and Perdue, of Georgia, initially unveiled the “Reforming American Immigration for a Strong Economy Act” in February, arguing that the bill will “help raise American workers’ wages by restoring legal immigration levels to their historical norms and rebalancing the system toward employment-based visas and immediate-family household members.”

“We are taking action to fix some of the shortcomings in our legal immigration system,” Perdue said at the time. “Returning to our historically normal levels of legal immigration will help improve the quality of American jobs and wages.”

Cotton’s office told CNN in July that the bill will be reintroduced with slight changes, but that the goal remains reducing legal immigration to the United States by 50%.

The proposed bill would cut back on “chain migration,” ways of immigrating to the United States that are based on family or not based on skills. The bill would limit the types of family members of immigrants that can also be brought to the US to primarily spouses and minor children, would eliminate the international diversity visa lottery and limit the number of annual refugee admissions.

“Over years, that has massively deskilled the migrant flow into America and produced all of those effects I’m talking about,” Miller said. “So, we’re proposing to limit family-based migration to spouses and minor children.”

The proposal would then establish a grading system for new immigrants where the prospective green card holders would be judged on their median salary, advanced degrees, ability to speak English, skills needed by the economy and whether you are able to afford your own health care.

“The effect of this, switching to a skills-based system and ending unfettered chain migration, would be over time you would cut net migration in half, whch polling shows supported overwhelmingly by the American people in very large numbers,” Miller said.

Julia Hahn, a special assistant to the President, and Andrew Bremberg, a policy aide, worked with Miller and Republicans on Capitol Hill on the measure.

Trump has long said he wants to reform the nation’s immigration system, but any plan to do that seems like less of a priority for an administration that is now focused on health care, tax reform and a host of international issues.

“What I’d like to do is a comprehensive immigration plan,” Trump told reporters aboard Air Force One in July. “But our country and political forces are not ready yet.”

This story has been updated.