(CNN) Republicans are bracing for the moment House Democrats formally request President Donald Trump's tax returns, attempting to fully understand the scope of a 1920s law that Democrats say gives them the power to obtain Trump's tax returns with a simple request.

Only one Democrat on Capitol Hill -- chairman of the House Ways and Means Committee Richard Neal -- has the power to request the return under the law. And even if he gets them, he doesn't unilaterally have the power to make them public without a vote of his committee. But, Neal has said he plans to ask for them. When exactly he will make that move is still under discussion.

Still, Republicans are beginning to set the groundwork for how they would have to respond if Democrats request a window into the President's closely-held financial holdings.

Senate Finance Committee Chairman Chuck Grassley, who also holds the power to request Trump's tax returns, has requested a briefing from the Joint Committee on Taxation about how section 6103, a provision in the IRS code that says a tax-writing chairman can request the tax returns of an individual -- would work.

Grassley's interest isn't in learning how to request the returns himself, but understanding how the process will work, the legal justifications behind it and the limits of the law as Democrats make their case that they are well within their rights to request the President's returns.

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