Federal prosecutors have directly asked witnesses in recent days about former President Donald J. Trump’s involvement in efforts to reverse his election loss, a person familiar with the testimony said on Tuesday, suggesting that the Justice Department’s criminal investigation has moved into a more aggressive and politically fraught phase…

Asking questions about Mr. Trump in connection with the electors plot or the attack on the Capitol does not mean the Justice Department has opened a criminal investigation into him, a decision that would have immense political and legal ramifications.

If a decision were made to open a criminal investigation into Mr. Trump after he announced his intention to run in the 2024 election, as he continues to hint he might do, the department’s leadership would be required to undertake a formal consultation process, then sign a formal approval of the department’s intentions under an internal rule created by former Attorney General William P. Barr and endorsed by Mr. Garland.

But in recent days, Mr. Garland has repeatedly asserted his right to investigate or prosecute anybody, including Mr. Trump, provided that is where the evidence leads.