Joe Kennedy speaks in Spanish as he tells Dreamers: 'We will fight for you and we will not walk away,' in State of the Union response

Joe Kennedy III, the Democrat selected to respond to Donald Trump's State of the Union address, broke into Spanish during his emotional speech, telling childhood immigrants to the US that their country would not walk away from them.

"To all the Dreamers watching tonight, let me be clear: Ustedes son parte de nuestra historia. Vamos a luchar por ustedes y no nos vamos alejar," the Representative from Massachusetts said.

In English, he added: "You are a part of our story. We will fight for you. We will not walk away."

Mr Kennedy was speaking specifically to the millions of immigrants who were brought to the US illegally as children – also known as Dreamers. Mr Trump announced he would wind down protections for these immigrants late last year, opening them up to the threat of deportation.

More recently, the President has used these protections as a bargaining chip with Democrats, saying he would allow some 1.8m childhood immigrants a path to citizenship in exchange for $25b for his proposed border wall with Mexico and other security measures.

In his State of the Union address, Mr Trump emphasised the need for increased border security, and even suggested ending a legal immigration programme sometimes called "chain migration". Democrats booed the President when he described chain migration – the practice in which immigrants' family members also come to the US – as allowing "virtually unlimited numbers of distant relatives" into the country.

In his rebuttal, Mr Kennedy assailed many of the President's other policies, from his attempts to repeal and replace Obamacare to his administration's rollback of protections for transgender students. He touched briefly on the issue of Russian meddling in the 2016 election – a sore spot for Mr Trump – and on the white supremacist rally in Charlottesville, Virginia.

Mr Kennedy even managed to work in his party's 2018 tagline, telling his audience that Democrats would choose a "better deal" for everyone who calls America home.

He closed by paying lip service to activist movements like "Me too," which sparked a national conversation about sexual harassment, and Black Lives Matter, which works to combat police brutality against black people.

"You bravely say, 'Me too'." You steadfastly say, 'Black lives matter'," the 37-year-old told his audience. "You wade through floodwaters, battle hurricanes, brave wildfires and mudslides to save a stranger."

He added: "You serve, you rescue, you help, you heal. That – more than any law or leader, debate work disagreement – that is what drives us towards progress."