"[M]oderate Democrats are worried that liberals in their own party are going to put forward articles of impeachment that are hard to vote for and even harder to explain voting for..."

"Democrats in politically difficult districts tend to favor writing charges that most closely hew to the Ukraine affair and might be most easy to explain to voters, while lawmakers from more solidly Democratic turf are feeling more adventurous and tend to want to reach out toward former special counsel Robert Mueller's Russia probe and other matters.... 'Judiciary’s not really reaching out to the people' whose political fates could rest on their impeachment votes, one senior Democratic aide close to party moderates said. 'There are 31 Democrats who are going to have to live, breathe and die this vote for the next year.'... Meanwhile Republican-aligned outside groups... have been trying to influence Democratic lawmakers by running advertisements and conducting polling in their districts..."

From "Why moderates are holding back on impeachment/Analysis: Some Democrats say they don't want to commit to articles they haven't seen" (NBC).