Barack Obama has praised the importance of “invisible” workers who underpin America in an apparent dig at the Republican immigration stance during his official portrait unveiling. The former US president said that the cleaners, food servers and garbage collectors who are so important to the country’s success are too often overlooked. He said such people “belong at the centre of American life” and warned against “simply celebrating the high and the mighty”. It comes as the Senate debates whether to grant citizenship to millions of migrants brought to America illegally while children, many of whom now work in the country. Mr Obama gave these so-called ‘dreamer’ migrants a path to citizenship while in office, however Mr Trump ripped up his presidential protections and instead handed the issue to Congress. Mr Obama was giving a rare public speech at the unveiling of the official portraits of himself and his wife Michelle at the Smithsonian National Portrait Gallery in Washington DC. His portrait, featuring Mr Obama sitting in a chair before a colourful background of leaves, was painted by Kehinde Wiley while Mrs Obama’s was done by Amy Sherald. Former President Obama and first lady Michelle Obama hold hands prior to portraits unveiling at the Smithsonian's National Portrait Gallery in Washington Credit: Reuters Discussing what impressed him about Mr Wiley’s past portraits, Mr Obama mentioned the way they “challenged our conventional views of power and privilege”. Mr Obama said the artist focused on “the beauty and the grace and the dignity of people who are so often invisible in our lives and put them on a grand stage, on a grand scale and force us to look and see them in ways that so often they were not”. He added: “People in our families, people who helped to build this country, people who helped to build this capitol, people who to this day are making sure that this place is clean at night and serving food and taking out the garbage and doing all the other stuff that makes this country work, so often out of sight and out of mind. “Kehinde lifted them up and gave them a platform and said they belong at the centre of American life and that was something that moved me deeply because in my small way that’s part of what I believe politics should be about. “Not simply celebrating the high and the mighty, expecting that the country unfolds from the top down but rather that it comes from the bottom up.” The comments, while not mentioning immigration or the Republican Party explicitly, come in a week when a fierce political battle about the future of undocumented migrants is playing out in Washington. .@MichelleObama: “I am humbled. I am honored. I’m proud. But most of all, I’m so incredibly grateful to all the people who came before me in this journey.” pic.twitter.com/Dyo6mBv5j8— Fox News (@FoxNews) February 12, 2018 The Senate is due to debate immigration legislation all week, though it remains unclear what proposals will be voted on or whether a majority can even be achieved. Mr Trump has proposed giving a path to citizenship for 1.8 million ‘dreamer’ migrants but only in return for $25 billion to fund his Mexican border wall and tighter rules on legal migration. Mr Obama has largely been reluctant to criticise Mr Trump since leaving in January 2016, in line with predecessors who have held their tongue. During the ceremony on Monday, Mr Obama also joked that he had asked for his portrait to have less grey hair and smaller ears than in real life, but the artist rejected his requests. Meanwhile Mrs Obama said she hopes an official portrait of her will serve as an inspiration to young black women who will see "someone who looks like them" hanging in Washington's National Gallery. Artist Amy Sherald and former first lady Michelle Obama participate in the unveiling of Mrs. Obama's portrait at the Smithsonian's National Portrait Gallery in Washington Credit: Reuters She told the audience: "I'm thinking about the young people, particularly girls and girls of colour who in years ahead will come to this place and they will look up and see an image of someone who looks like them…I know the kind of impact that will have on their lives, because I was one of those girls." The paintings were unveiled on Monday at the gallery, which is part of the Smithsonian group of museums. The gallery has a complete collection of presidential portraits. In an emotive speech, Mrs Obama said: "I've never had any portrait done let alone a portrait that will be hanging in the National Gallery. But all those folks who helped me be here today, they're with us physically and in spirit. "I'm thinking of my grandparents… they were all highly intelligent capable men and women. Their dreams and aspirations were limited because of the colour of their skin. Artists Sherald and Wiley gather with Hanks prior to unveiling of Obamas' portraits at the Smithsonian Credit: Reuters "I'm thinking of my dad, who sacrificed everything for me and my brother. And I'm thinking of my mum… always putting herself last. "I'm also thinking of the young people, the young girls who in the years ahead who will come here and see someone who looks like them hanging on the wall of this great institution. And I know what kind of impact that will have on their lives, because I was one of those girls." In a reference to the current political climate, Mrs Obama said: "We have come so far, and yes, as we see today we still have a lot more work to do. But we have every reason to be hopeful and proud."