So why do Democrats require IDs to buy guns but oppose them for voting?

The Washington Post has a piece on North Carolina's new voter ID law:

. . . The measure requires voters to present government-issued photo identification at the polls and shortens the early voting period from 17 to 10 days. It will also end pre-registration for 16- and 17-year-old voters who will be 18 on Election Day and eliminates same-day voter registration.
Democrats and minority groups have been fighting against the changes, arguing that they represent an effort to suppress the minority vote and the youth vote, along with reducing Democrats’ advantage in early voting. They point out that there is little documented evidence of voter fraud. . . .
The Justice Department has suggested it will fight the new law, which comes just weeks after the U.S. Supreme Court struck down a key portion of the Voting Rights Act. States like North Carolina are no longer required to obtain preclearance from the Justice Department for such changes after the Court struck down the formula used for determining which states and jurisdictions with a history of voter suppression require preclearance.
The Justice Department is also looking to challenge a new Voter ID law in Texas and has also fought against a new Voter ID law in Florida. . . .

So where are the DOJ lawsuits over requiring IDs to buy guns?  Don't they also discriminate minorities?