WASHINGTON — House Democrats unveiled on Friday the details of ambitious legislation devised to lower barriers to the ballot box, tighten ethics and lobbying restrictions and, in a swipe at President Trump, require presidents and candidates for the nation’s highest offices to release their tax returns.

Singling out Mr. Trump and his administration, Democrats said that they were making good on promises to voters across the country who vaulted them into the majority with demands to clean up corruption and influence-peddling in Republican-controlled Washington.

“Over the last two years, President Trump set the tone from the top of this administration that behaving ethically and complying with the law is optional,” said Representative Elijah Cummings of Maryland, the chairman of the House Oversight and Reform Committee. “Ladies and gentlemen, I have stopped by here to simply say we are better than that.”

Little if any of the bill, named H.R. 1 to underscore its primacy, is likely to become law; in its sprawl and ambition, the measure is less a legislative vehicle than a political platform for the Democrats heading into the 2020 presidential cycle.