Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.) fired back at President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s offer to pay her $1 million to take a test to prove her Native American heritage on Thursday by invoking his administration’s use of DNA tests to reunite separated immigrant parents and children.

“Hey, @realDonaldTrump: While you obsess over my genes, your Admin is conducting DNA tests on little kids because you ripped them from their mamas & you are too incompetent to reunite them in time to meet a court order,” Warren tweeted.

“Maybe you should focus on fixing the lives you're destroying.”

Hey, @realDonaldTrump: While you obsess over my genes, your Admin is conducting DNA tests on little kids because you ripped them from their mamas & you are too incompetent to reunite them in time to meet a court order. Maybe you should focus on fixing the lives you're destroying. — Elizabeth Warren (@elizabethforma) July 5, 2018

The Department of Health and Human Services (HHS) said Thursday that it was conducting DNA tests to more quickly reunite immigrant children separated from their parents at the border under a since-ended administration policy.

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Trump said at a campaign rally Thursday that if he were debating Warren, he would offer her $1 million to take an ancestry test to back up her past claims of Native American heritage.

“And we will say, ‘I will give you a million dollars, paid for by Trump, to your favorite charity if you take the test and it shows you’re an Indian,'” Trump said. “And we’ll see what she does. I have a feeling she will say no but we will hold it for the debates.”

Trump has repeatedly attacked Warren using the name “Pocahontas” since the days of his presidential campaign.

Warren has stood by her claims of Native American heritage, which is not documented, saying earlier this year that she knows “who I am.”

“Look, I do know. I know who I am. And never used it for anything. Never got any benefit from it anywhere," Warren said at the time. Warren's critics allege she obtained past academic positions in part because she claimed to be part of a minority.