At Monday’s judiciary hearing, Sen. Lindsey Graham (R-S.C.), chairman of the subcommittee on crime and terrorism, asked former director of national intelligence James Clapper about President Trump’s finances:

GRAHAM: General Clapper, during your investigation of all things Russia, did you ever find a situation where a Trump business interest in Russia gave you concern?
CLAPPER: Not in the course of the preparation of the intelligence community’s assessment.
GRAHAM: Since?
CLAPPER: I’m sorry?
GRAHAM: At all, any time?
CLAPPER: Senator Graham, I can’t comment on that because that impacts an investigation.

Graham later made clear what he is looking for and why it’s important. Graham told a CNN reporter, “I want to know more about Trump’s business dealings. I asked Clapper. I said, ‘Is there any business dealings with the Trump organization that gave you concern?’ And he said, ‘No,’ with a caveat, ‘I don’t know what the FBI is looking at so I don’t want to run afoul with them.'” Graham added, “Trump has said he never did business with the Russians.” Asked if looking at Trump’s tax returns could be helpful to an investigation, he responded, “It could be, down the road.”

Let’s be frank: If Trump had Russian business deals and was lying, he, just like former national security adviser Michael Flynn, would be compromised; the Russians would know what he is saying is not true and they would therefore have leverage over the president of the United States. That’s quite apart from whether Trump might have felt financial pressure or incentive to treat the Russians more gently than he otherwise would. Potential Russian ties or concerns certainly may have affected the way he treated Flynn after being told Flynn was lying to the vice president about contacts with the Russians. Any Russian connection very well could have made Trump more reluctant to cut Flynn loose. We simply don’t know, because Trump is not letting us look at available evidence.

Graham, a former military lawyer, knows precisely what he is doing. In the legal context, during the “discovery phase,” one side is allowed to look at all relevant evidence or at evidence that might reasonably lead to relevant evidence. That is effectively what Congress is charged with — finding and explaining relevant evidence of Russian connections to Trump and his campaign. Surely Trump’s business ties, if any, and his possible untruthfulness are germane to the investigation.

Lots of documents and individuals might be able to shed light on these matters: Trump’s sons (who have said the Russians played a big part in Trump’s real estate business), his accountant and his business records, including tax records. Press secretary Sean Spicer suggested at the White House briefing that some sort of letter might be coming from his lawyer. Terrific. That person can then be questioned under oath. (What records did Trump make available? What Russian oligarchs bought Trump properties? What did Trump’s son mean in statements suggesting Russia played a big part in their family business?) The issue is not simply current connections (which even Trump would not maintain) but past deals, loans, partnerships, etc.

If the FBI investigators isn’t already looking for financial ties between Trump (as well as his campaign and transition officials) and Russians, they aren’t doing a very thorough job. Whether they are pursuing such avenues of inquiry or not, Graham and other members of relevant Senate committees have every reason — and, I would suggest, the obligation — to present a full picture of Trump’s Russia associations to the American people.

If the other party had the majority, we’d already have seen subpoenas and/or legislation requiring disclosure of Trump’s tax returns. That might happen after the 2018 election, but in the meantime Graham is right to want to know everything about Trump campaign ties to the Russians — and that must include all the candidate’s ties, including financial ones.