California is suing the Trump administration over its planned border wall with Mexico, the latest salvo in the state’s ongoing battle with the federal government.

The lawsuit takes aim at one of Donald Trump’s signature campaign promises, a proposal that galvanized conservative voters angry about illegal immigration and rallied fierce resistance from pro-immigrant forces in deep blue California. The state is home to America’s largest population of undocumented immigrants and governed by an unbroken Democratic government.

According to a lawsuit filed by California Attorney General Xavier Becerra and the California Coastal Commission, Mr Trump’s wall proposal violates federal environmental protections and illegally seeks to circumvent state law. Earlier this year the administration moved to waive a variety of mostly environmental statutes “to ensure the expeditious construction of barriers and roads” in the US-Mexico border area near San Diego.

“No one gets to ignore the laws. Not even the president of the United States”, Mr Becerra said during a press conference in San Diego. “We respect immigration policy. We understand it’s a federal matter. But if it happens in our backyard we demand it be carried out in the right way, following the rule of law” he added.

To build the wall, the Trump administration would need to persuade a Congress has so far proved reluctant to allocate the needed funding. Lawmakers were unmoved by Mr Trump's threat to shut down the government if a budget deal did not pay for the wall. The administration sought to highlight progress in announcing it had awarded contracts to design the wall.

Since announcing that he was negotiating an immigration deal with Democratic leaders, Mr Trump has sent mixed messages on whether wall funding would need to be part of any agreement. Democrats have rejected such a pact, and they are facing intense grassroots pressure to not concede ground as they negotiate with a president who has antagonized immigrants.

Life on the US-Mexican border Show all 12 1 /12 Life on the US-Mexican border Life on the US-Mexican border Tijuana, Mexico A house stands next to a section of the border fence separating Mexico and the US Reuters Life on the US-Mexican border Tijuana, Mexico The border fence in Tijuana stretches all the way to beach Reuters Life on the US-Mexican border Tijuana, Mexico Migrants can often be spotted trying to cross the rusty barrier Reuters Life on the US-Mexican border Tijuana, Mexico Joaquin, 36, a chef from Guatemala who says he was deported from the US Reuters Life on the US-Mexican border Tijuana, Mexico A shack stands next to a section of the border fence Reuters Life on the US-Mexican border Tijuana, Mexico Tourists pose for a picture at the border Reuters Life on the US-Mexican border Tijuana, Mexico A family burns rubbish near the fence Reuters Life on the US-Mexican border Tijuana, Mexico Joaquin makes a living by selling rubbish Reuters Life on the US-Mexican border Tijuana, Mexico ‘Neither Trump nor the wall is going to stop anyone,’ says Pedro Reuters Life on the US-Mexican border Tijuana, Mexico Mexicans have built homes right next to the fence Reuters Life on the US-Mexican border Tijuana, Mexico Mexican Carlos, 27, who says that he was deported from the United States, heats up tortillas at his house near the double fence that separates Mexico and the US Reuters Life on the US-Mexican border Tijuana, Mexico A girl climbs stairs near a section of the fence

The project would also need to surmount a growing wall of legal challenges. Even before Mr Becerra's announcement, multiple environmental groups had already sought to block the project in court.

But as the top law enforcement official in the nation's most populous state, Mr Becerra has a unique platform from which to confront the Trump administration. By asserting the federal government has overstepped its authority, Mr Becerra continued to assert California’s sovereignty in the face of a hostile federal government.