(CNN) House Speaker Nancy Pelosi told Democrats in a private meeting Wednesday that she wants to focus their impeachment inquiry on President Donald Trump's conversations with Ukraine, as members debate how broadly to draft articles of impeachment, according to several sources involved in the discussions.

Despite months of focus on former special counsel Robert Mueller's findings and allegations of obstruction of justice, Pelosi and top Democrats believe their strongest case for impeachment to the American public is the President's ask that the Ukrainians investigate his political rival, former Vice President Joe Biden.

That means if Democrats draft articles of impeachment, they are likely to be focused on the Ukraine controversy — not on allegations that Trump tried to thwart the Mueller probe. A broader resolution could make it more complicated to get the votes on the floor, according to multiple Democratic sources. But discussions about the scope of the articles of impeachment are ongoing.

At a private caucus meeting Tuesday where Pelosi explained her decision to embrace impeachment proceedings, the House speaker was asked about Democrats' other ongoing investigations, which she said would continue. But sources said she stressed the Ukraine controversy, characterizing it as a betrayal of the President's oath of office.

JUST WATCHED Pelosi on impeachment inquiry: No one is above the law Replay More Videos ... MUST WATCH Pelosi on impeachment inquiry: No one is above the law 02:43

Publicly, Democrats are debating how far to go in drafting the resolution, as well. Going too broad in articles of impeachment, Democrats fear, could become unwieldy and cost them crucial support, especially among a slew of moderate freshmen who have only embraced impeachment in the aftermath of the Ukraine controversy.

Read More