WASHINGTON — Fresh off a midterm election that has given them control over levers of congressional oversight, Democrats have made clear they plan to step up their efforts to monitor special counsel Robert Mueller’s Russia investigation.

But that’s just one of a myriad of issues they are planning to aggressively pursue.

For two years, House Democrats trying to police the Trump administration have pressed the White House, cabinet officials and others for answers on issues ranging from the treatment of undocumented immigrants to potential Trump family conflicts of interest. Little of that outreach, coming in the form of official letters from the minority party, ever got a response.

As they prepare to ascend to the House majority, Democrats are using a trove of more than 100 letters — rejected or ignored by Republican committee leaders and federal agencies — as a template to map their approach to oversight in the new Congress.

Those letters, assembled as a 67-page document by House Judiciary Committee Democrats, were shared with NBC News.

Aside from the investigation into Russian attempts to meddle in the 2016 election, top Democratic leaders insist they also want to prioritize oversight around things that matter most to the American people, including health care.

Yet the Democrats who will actually chair the chamber’s most powerful committees say they will use their new powers to pursue many questions and requests that have gone unanswered until now. "The American people voted to give the House of Representatives a mandate" to conduct "credible" investigations, Maryland Democrat Elijah Cummings, the incoming House Oversight Committee chair, said after Democrats flipped the House on Tuesday.

Cummings’s office said that until now, the committee under GOP control has stalled most investigations. The current chairman, Rep. Trey Gowdy, R-S.C., has issued just one subpoena — to a Department of Homeland Security career employee — and blocked 64 motions by Democrats, even as the administration hasn’t answered dozens of document requests. Gowdy issued 14 subpoenas during the Benghazi Committee investigating former 2016 presidential candidate Hillary Clinton. Gowdy's office did not respond to requests to comment.

The 64 denied motions relate to issues ranging from news reports that members of Trump’s Mar-a-Lago resort may have influenced policy decisions to the Agriculture Department’s communications with corporate lobbyists and foreign payments to the Trump Organization.

Guide to the probes

The letters provide a sampling of Democrats' priorities. Many reflect the interests of the incoming House Judiciary Committee Chairman, New York Democratic Rep. Jerrold Nadler, while several dovetail with areas that Cummngs has pursued.

Issues reflected in the letters include the rise of white supremacist violence; the administration’s treatment of undocumented immigrants at the U.S.-Mexico border; and Trump family conflicts of interest, including potential violations of the Emoluments Clause to the U.S. Constitution that prohibit a president from profiting from the office.

White Supremacy: Early in the Trump administration, officials froze $10 million in funding granted to several groups dedicated to combating white supremacist and neo-Nazi movements. A Feb. 22, 2017 letter signed by over 150 Democrats and Republicans urged the Departments of Justice and Homeland Security to address “threats to Jewish organizations” after bomb threats had been telephoned in to Jewish community centers across the nation. Days before the 2018 midterms, a gunman opened fire at a Pittsburgh synagogue, killing 11 and wounding six, in the deadliest attack on Jews in U.S. history.

Immigration: In April, a bipartisan group of 32 House members sent a letter to then DHS-secretary John Kelly requesting information on how immigrant victims of crimes such as human trafficking would be protected in light of Trump’s executive orders pertaining to interior and border enforcement. On Oct. 26, another letter from Democrats on the subcommittee on immigration to Acting Secretary of Homeland Security Elaine C. Duke expressed concern regarding the detention of a 10-year old with cerebral palsy immediately after being released from surgery.

Other letters pertained to the termination of programs providing "critical legal assistance" to detained immigrants. One year after the initial letter, and following Trump’s creation of numerous detention centers at the border, the DHS responded in a four-page letter, the report notes, while listing a host of additional pending inquiries about detention centers that have become controversial.

Healthcare: In a letter dated June 2018, Democrats raised "serious concerns" about the administration’s decision not to defend key protections of the Affordable Care Act from a legal challenge filed in Texas by a coalition of Republican-led states. The letter insisted that the administration is obligated to "defend" the nation’s health care law from the attempt to invalidate it. The Trump administration has decided not to defend several important provisions including those that would gut protections for those with preexisting conditions.

Conflicts of Interest: Several letters hint at the kind of conflicts-of-interest inquiries Democrats will initiate against the Trump family.

On May 3, 2017 in a letter to the Ivanka Trump Collection, Judiciary Democrats asked that Ivanka Trump, the president’s daughter and a White House senior adviser, recuse herself from any "particular matters affecting her financial interests" given her role as an adviser to the president. Before and after Ms. Trump accepted her position, she participated in meeting with officials from countries like Japan and China in which she "has significant financial interests — including pending licensing deals and trademark applications," the letter states. Also that month, they inquired about Trump’s financial ties to China following his advocacy for Chinese telecommunications firm ZTE.

A day before Tuesday’s midterm election, the left-leaning Citizens for Responsibility and Ethics in Washington reported Ivanka Trump’s fashion brand received first approval for 16 new trademarks from the Chinese government in October.

How the Democrats proceed with trying to obtain Trump’s federal tax returns remains the big unknown.

Trump is likely to fight any request by the House Ways and Means Committee to the Internal Revenue Service for his tax returns, which could force a prolonged legal standoff.

"The American people will see his tax returns, not because of voyeuristic interest, but because they should know if he is corrupt. We will look at the cashing-in of access to the Oval Office," said Eric Swalwell, a California Democrat who sits on the Judiciary Committee.

Matt Miller, who served at the Justice Department under Obama during the Republicans’ 2010 House takeover, said the Democrats’ requests are likely to create a significant strain for federal agencies that have been subject to scant oversight by the GOP-led Congress.

"It is a significant drain on the time of senior officials and there’s an opportunity cost because you can’t focus on your agenda," said Miller.

And, he added, "if you have any real liability there’s this drip, drip, drip before hand that is paralyzing and can be fatal."