U.S. President Donald Trump ushered in America's 250th anniversary of independence Friday with a speech at Mount Rushmore that swerved from soaring rhetoric about American exceptionalism into a pointed attack on what he called the "communist" threat rising within the country. "Communism is a mortal threat to American liberty," he said at the South Dakota monument. "It is the greatest threat to our country, including World War I, World War II, Pearl Harbor or even 9/11." "There is now a resurgence of the communist menace in our land, including from newcomers to our country who embrace ideas totally opposed to our way of life and our great success," Trump said, tying his anti-communist rhetoric to the anti-immigrant themes that fueled his election. At one point he said the "newcomers" needed to be expelled. "We resolve and swear for all to hear that the citizens of the United States of America will vanquish communism quickly," he said. "We will send them quickly away, and we will continue to build our country bigger and better, stronger than ever before. America will never be a communist country!" He then pivoted immediately to the political stakes: "We can only lose the midterms if we allow ourselves to lose the midterms." The speech comes as Republicans grow increasingly uneasy over a string of wins by progressive and democratic socialist candidates. Four won competitive Democratic primaries in New York City last week and in Colorado on Tuesday, with additional victories in Kentucky, New Jersey, Ohio, Pennsylvania and Texas. Last week Trump called those wins "the greatest threat to our country since its founding." Mamdani responds without naming him In New York, Mayor Zohran Mamdani, a democratic socialist, delivered his own address describing America as a nation of contradictions "working each day towards the perfection in which it was conceived." Without mentioning Trump by name, Mamdani appeared to address the president's divisive rhetoric directly: "For generation after generation, we have been told that when the world has sent its people to our shores, it has not sent its best. Those ideals upon which our nation was built — they are strong enough to endure any authoritarian regime, but only if we reach for them." Heat disrupts the holiday An extreme heat wave has upended Fourth of July celebrations across much of the eastern United States. Philadelphia canceled its Salute to Independence parade. The Great American State Fair on the National Mall in Washington shut down early in the afternoon before reopening at 5 p.m. The Capitol Fourth concert went ahead regardless, featuring Patti LaBelle, Trace Adkins and members of the Artemis II space mission, with fireworks over George Washington's Mount Vernon. An Independence Day parade scheduled for Saturday in Washington was canceled. At Mount Rushmore, by contrast, temperatures stayed a cool 65 degrees Fahrenheit. Freedom 250, an organization aligned with the White House, has organized much of the Washington programming in rivalry with America250, the bipartisan group founded by Congress a decade ago that is behind ball-drop celebrations in cities including New York. According to an April survey by the Associated Press-NORC Center for Public Affairs Research, roughly four in ten American adults say they feel "proud" of the 250th anniversary, while about three in ten say "excited" describes their feelings.