But by far the biggest thing Democrats want, now that they have the majority in the House, is to get their hands on the president's tax returns.
House Democrats want to use a 1924 law that allows any one of three entities -- the House Ways and Means Committee, the Senate Finance Committee or the Joint Committee on Taxation -- to demand that the Treasury Department turn over the returns of any individual. The law has almost never been used.
For the first 50 years of its existence, no one tried to get a president's returns -- although the law played a role in the fight over Richard Nixon's finances -- and in the years since Gerald Ford took office, presidents have voluntarily made their returns public. Until Donald Trump.
So now, Democrats propose that the entity they fully control -- the Ways and Means Committee -- force Treasury, parent agency of the Internal Revenue Service, to turn over the president's returns. What do they hope to find? What is remarkable is that even the most aggressive Democrats don't seem to have a clear idea what they will find in the returns. They're just sure there must be something bad in there.
The former prosecutor Andrew McCarthy has written of Trump-Russia special counsel Robert Mueller that "Mueller does not have a crime he is investigating. He is investigating in hopes of finding a crime." That is what Democrats are planning with the president's tax returns.
"President Trump's refusal to release his tax returns makes it clear he has something to hide," said Democratic Sen. Tammy Baldwin, who is a sponsor of the Presidential Tax Transparency Act, which would require presidents and presidential candidates to release their returns.
Of course, Democrats do have some broad ideas about what might be in the returns.
"We want to see if the president of the United States has a conflict of interest that he brought with him or that he created since he got here," Rep. Bill Pascrell, a member of Ways and Means, said recently. "The only way to do that is to get his tax returns."
Others think -- no surprise -- that there's a Russia connection. Rep. Jackie Speier, a member of the Intelligence Committee, said it is important "for the American people to know to what extent Russia was engaged with then-entrepreneur Donald Trump. ... Was there money laundering going on? ... That's why having his tax returns becomes so important."
Other Democrats want the tax returns to see if Trump might have violated the "emoluments clause" of the Constitution. Still others want to see if Trump got a special break in the tax cut law he signed.
Democratic Rep. Maxine Waters, chair of the Financial Services Committee, was the most blunt. "We're gonna get your tax returns," Waters said recently, addressing Trump. "We're gonna find out where your money has come from, the way that you have cheated the IRS."
The tax returns -- many House Democrats believe -- will be a Rosetta Stone to Trump corruption.
There's no doubt the law gives Ways and Means Chairman Rep. Richard Neal the power to demand the returns. That doesn't mean Neal would get them right away; the Trump administration would surely raise legal objections that could tie the issue up in court. Perhaps for that reason, Neal has been a voice of caution in the push to see the returns.
There are others, too. Democratic Rep. Ron Kind, also a Ways and Means member, recently remarked that Mueller and his prosecutors have surely seen the returns, and therefore it would be best for the House to proceed carefully. But that is precisely what worries some Democrats. What if Mueller investigates and does not accuse Trump of any wrongdoing based on the tax returns?
Just in case, Democrats propose to perform an "MRI" on Trump's finances, based in large part on the tax returns.
"Our priority is to make sure the president of the United States is working in the national interest, that he is not motivated by some pecuniary interest or fear of compromise or actual compromise," Intelligence Committee Chairman Rep. Adam Schiff said recently. "What we're interested in is: Does the president have business dealings with Russia such that it compromises the United States?"
For the Democrats to start the "MRI," the first step has to be securing the president's returns.
Trump broke a 40-year tradition by not releasing his tax returns during the campaign or since. Now, there are bills in both the House and Senate that would require presidents, and party nominees for the presidency, to release their returns. But they're not law yet, and might never be.
Whatever happens, there will likely be serious consequences if the Ways and Means Committee chooses to force the release of the president's returns. For one, it will set a precedent for the House majority, in this case the Democrats, to go after the tax returns of individuals. It is not hard to imagine that coming around to bite Democrats in the future.
Nevertheless, that is what Democrats appear to want. At a recent Ways and Means hearing into the issue of acquiring individual returns, Rep. John Lewis summed up the situation, and in the process said perhaps more than he intended: "This is not the end," Lewis said. "This is just the beginning."