Shortly after Trump took office on Monday, the American Civil Liberties Union, Democratic attorneys general, immigration activists, and members of the progressive “Squad” mobilized to challenge Trump legally or in the court of public opinion.

At a progressive Democratic press conference Wednesday afternoon, Rep. Delia Ramirez (D-IL) and others vowed to “fight” Trump over a number of his policy changes, including the citizenship issue.

“Our communities are precious, and our coalition is ready to organize, to be in the streets, informing our community about their constitutional rights, and we’re also ready to fight like hell for the people we love,” Ramirez said.

Rep. Ilhan Omar (D-MN) said Trump’s executive action to rescind birthright citizenship was not only unsound but was being met by valid blowback.

“I do believe his executive order to end birthright citizenship is illegal and unconstitutional, that it should be challenged. I am really proud of folks around this country who responded so, so readily,” Omar said, while introducing legislation to repeal the Alien Enemies Act of 1798 used as justification for Trump’s immigration orders.

The sudden surge of lawsuits against the Trump administration, including from 18 Democratic state attorneys general and the ACLU earlier this week, is reminiscent of 2017, when Trump was hit hard by left-leaning groups infuriated by what they viewed as anti-immigrant and discriminatory executive actions that focused on enhancing border security and maintaining the legitimacy of the immigration system.

Cecillia Wang, national legal director at the ACLU, said they chose to sue first over the birthright citizenship executive order because it was a constitutional matter.

“We are working hard on bringing other lawsuits,” Wang said during an interview Tuesday with CNN’s Kate Bolduan. “We moved with this lawsuit first because this is one of President Trump’s first salvos, not only against American communities, including immigrant members of our communities, but also he’s fundamentally striking at one of the promises of the American Constitution after the Civil War.”

“Through the 14th Amendment, one of the Reconstruction amendments, the framers of the Constitution made it clear that regardless of your parents’ nationality, your parents’ status, everyone born on American soil is a U.S. citizen,” Wang said.

The 43 Democrats on the House’s Congressional Hispanic Caucus lamented the move as “un-American and unconstitutional.”

The president of the nation’s largest and oldest Latino civil rights organization, the League of United Latin American Citizens, said upholding the Constitution was the basis for the group’s concerns over who could become a U.S. citizen.

“While we support sound immigration policies, we must uphold the United States Constitution,” said Roman Palomares, LULAC’s national president and board chairman, in a statement. “Any attempt to undermine the constitutionally protected birthright of those born in this country is an affront to both our laws and human decency.”

LULAC CEO Juan Proaño went a step further and said Trump’s order was such an affront that he viewed it as an attempt “to demonize brown and black immigrants.”

“If not stopped, it will undermine the very essence of what it means to be an American and will tear families apart,” Proaño said.

World Relief, an organization that works with migrants and refugees globally, said it opposed the idea of rescinding the 14th Amendment because it was outside of Trump’s legal authority to do so.

“There is a process to amend the U.S. Constitution, of course, but this is not it,” Matthew Soerens, vice president of advocacy and policy at World Relief, said in a statement. “In any case, such a change would be shortsighted. Birthright citizenship has served the United States well.”

At least 11 million immigrants are residing in the country illegally, meaning children born to any of those people would be given U.S. citizenship.

“Had their children also been born without legal status, we’d have far more individuals residing unlawfully in our country, denied both the rights and responsibilities of citizenship and prohibited from fully contributing to what — thanks to the 14th Amendment — is their country as much as it is any other American’s,” Soerens said.

While Democrats and left-leaning groups vowed to fight, Republicans moved forward with codifying Trump’s plan into law.

Rep. Brian Babin (R-TX) introduced a bill to end birthright citizenship.

“America’s citizenship laws should reflect fairness and respect for the rule of law,” Babin said in a statement. “This common-sense legislation corrects decades of misuse and closes the loophole that incentivizes illegal immigration and exploits U.S. citizenship through birth tourism. Citizenship is one of our nation’s most precious privileges.”

This is not the first time Trump has faced problems walking back birthright citizenship.

In October 2018, the president insisted that birthright citizenship “will be ended one way or the other,” opening the door for congressional action after then-House Speaker Paul Ryan said that doing so by executive action was unconstitutional. The effort did not move forward.

Hailey Bullis contributed to this report.