Cummings was a formidable orator who advocated for the poor in his black-majority district , which encompasses a large portion of Baltimore and more well-to-do suburbs.
As chairman of the House Oversight and Reform Committee, Cummings led investigations of the president's government dealings, including probes in 2019 relating to Trump's family members serving in the White House.
Trump criticized the Democrat's district as a "rodent-infested mess" where "no human being would want to live." The comments came weeks after Trump drew bipartisan condemnation following his calls for Democratic congresswomen of color to go back to their "broken and crime-infested countries."
Cummings replied that government officials must stop making "hateful, incendiary comments" that distract the nation from its real problems, including mass shootings and white supremacy.
"Those in the highest levels of the government must stop invoking fear, using racist language and encouraging reprehensible behavior," Cummings said.
On Thursday, Trump ordered flags at the White House, military bases and other federal buildings to be flown at half-staff through Friday to honor Cummings. He also tweeted his "condolences to the family and many friends of Congressman Elijah Cummings. I got to see firsthand the strength, passion and wisdom of this highly respected political leader." The tweet made no reference to past feuds.
Former President Barack Obama, whose 2008 presidential bid counted Cummings as an early supporter, said he and his wife, Michelle, were "heartbroken" by the loss of their friend.
"As Chairman of the House Oversight Committee, he showed us all not only the importance of checks and balances within our democracy, but also the necessity of good people stewarding it," Obama said in a statement, describing Cummings as "steely yet compassionate, principled yet open to new perspectives."
In a joint statement, former President Bill Clinton and his wife, former Secretary of State Hillary Clinton, also praised Cummings' leadership of the committee "in finding facts, exposing fictions, and demanding that our government be accountable."
Congressman and civil rights leader John Lewis said that with Cummings' death, Americans "have lost a great leader at a time of crisis in our democracy."
"When this nation needed him most, he became a moral voice 'crying in the wilderness,' and his words and actions called a reluctant nation to conscience," the Georgia Democrat said in a statement.
Cummings' career spanned decades in Maryland politics. He rose through the ranks of the Maryland House of Delegates before winning his congressional seat in a 1996 special election to replace Kweisi Mfume, who left to lead the NAACP.
By 2016, Cummings was the senior Democrat on the House Benghazi Committee, which he said was "nothing more than a taxpayer-funded effort to bring harm to Hillary Clinton's campaign."
Throughout his career, Cummings used his fiery voice to highlight the struggles and needs of inner-city residents. He believed in much-debated approaches to help the poor and addicted, such as needle exchange programs to reduce the spread of AIDS.
A key figure in the Trump impeachment inquiry , Cummings had hoped to return to Congress within about a week after a medical procedure for which he didn't offer details. He'd previously been treated for heart and knee issues.
Cummings' committee, authorized to investigate virtually any part of the federal government, is one of three conducting the House impeachment probe of Trump. Cummings was among the three chairmen to sign a letter seeking documents into whether Trump pressured Ukraine to investigate the family of Democratic presidential rival Joe Biden, the former vice president. The committees have issued subpoenas of witnesses after the Trump administration's refusal to cooperate with the impeachment probe and have jointly been meeting behind closed doors to hear testimony.
Rep. Carolyn Maloney, a veteran Democrat from New York, will for now take over leadership of the House oversight committee, according to a senior Democratic leadership aide who spoke on condition of anonymity to discuss the decision publicly.
Separately, Cummings led an effort to gain access to Trump's financial records. His committee subpoenaed records from Mazars USA, an accounting firm that provided services to Trump. The panel demanded documents from 2011 to 2018 as it probed Trump's reporting of his finances and potential conflicts of interest. Last week, a federal appeals court ruled the records must be turned over.
Cummings' office said he died early Thursday at Johns Hopkins Hospital, and constituents began mourning soon after.
His widow, Maya Rockeymoore Cummings, chairwoman of Maryland's Democratic Party, said in a statement: "He worked until his last breath because he believed our democracy was the highest and best expression of our collective humanity and that our nation's diversity was our promise, not our problem."
Cummings was born Jan. 18, 1951. In grade school, a counselor told Cummings he was too slow to learn and spoke poorly, and would never fulfill his dream of becoming a lawyer.
"I was devastated," Cummings told The Associated Press in 1996, shortly before winning his seat in Congress. "My whole life changed. I became very determined."
It steeled Cummings to prove that counselor wrong. He became not only a lawyer, but one of the most powerful orators in the statehouse, where he entered office in 1983. He rose to become the first black House speaker pro tem. He would begin his comments slowly, developing his theme and raising the emotional heat until it became like a sermon from the pulpit.
Cummings was quick to note the differences between Congress and the Maryland General Assembly, which has long been controlled by Democrats.
"After coming from the state where, basically, you had a lot of people working together, it's clear that the lines are drawn here," Cummings said shortly after entering Congress in 1996.
Cummings began his long push for civil rights at age 11, when he helped integrate a swimming pool in Baltimore. This year, during a speech to the American Bar Association in April, Cummings recalled how he and other black children organized protests with help from their recreation leader and the NAACP.
Every day for a week, when the children tried to get into the pool, they were spit upon, threatened and called names, Cummings said; he said he was cut by a bottle thrown from an angry crowd.
"The experience transformed my entire life," he said.
While serving in the Maryland House of Delegates from 1983 to 1996, Cummings pushed for a ban on alcohol and tobacco ads on inner-city billboards in Baltimore, leading to the first such prohibition in a large U.S. city.
Cummings then chaired the Congressional Black Caucus from 2003 to 2004, employing a hard-charging, explore-every-option style to put the group in the national spotlight.
He cruised to big victories in the overwhelmingly Democratic district, which had elected Maryland's first black congressman, Parren Mitchell, in 1970.
In 2015, when the death of black Baltimore resident Freddie Gray sparked the city's worst riots in decades, Cummings carried a bullhorn in the streets and urged crowds to go home and respect a curfew. He spoke at Gray's funeral, asking lawmakers in the church to stand up to show Gray's mother they would seek justice.
"I want justice, oceans of it. I want fairness, rivers of it. That's what I want. That's all I want," Cummings said, quoting from the Bible.
Witte reported from Annapolis. Associated Press Writer Alan Fram contributed from Washington.
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