Ben Jealous has promised to do a lot of things. We didn't expect gerrymandering to be one of them.

We get the rah-rah nature of political party unity rallies. A party’s leaders are expected to fire up the troops with promises to win big up and down the ballot, and sometimes they go a little too far, like Senate President Thomas V. Mike Miller’s boast several years ago that Democrats would “bury Republicans” face down, six feet under ground. Democratic gubernatorial candidate Ben Jealous’ promise at a Baltimore County unity rally on Thursday to eliminate Republicans altogether from Maryland’s Congressional delegation might be chalked up as mild by comparison.

Except for one thing: He wasn’t just talking big, he was making a policy pronouncement about redistricting. “Our congressional delegation is on the ballot this November — not just their re-election, but their districts,” he said referring to the fact that the next governor will play the prime role in redrawing congressional (and, for that matter, legislative) districts after the 2020 Census. Mr. Jealous said that if elected, he would make sure Maryland sent eight Democrats to the House of Representatives while predicting that Gov. Larry Hogan, if re-elected, would draw the lines in a way that would result in a delegation split evenly between Democrats and Republicans. Quite explicitly, Mr. Jealous is promising to use gerrymandering for partisan aims.

A spokesman later told The Sun’s Luke Broadwater that the Democrat intends to maintain the seven districts currently represented by Democrats and to attempt to take out the delegation’s lone Republican, Rep. Andy Harris, by campaigning against him. But that means maintaining what are already some of the most absurdly gerrymandered districts in the nation, ones drawn with the explicit purpose of increasing the Democrats 6-2 edge to 7-1. Former Gov. Martin O’Malley said so in sworn testimony in a court challenge to the districts, yet he has recognized that it was wrong. Mr. Jealous, not so much.

If Governor Hogan is re-elected and manipulates the maps as Mr. Jealous suggests, it will be Democrats’ own fault. He has repeatedly proposed the creation of an independent, non-partisan commission to redraw congressional and legislative district lines only to have the idea killed in the Democrat-controlled legislature. Apparently the Democrats were banking on his defeat at the polls this year.

Even with the possibility before him that he could help his party through gerrymandering, Mr. Hogan reiterated his support for reform on The Sun’s endorsement questionnaire, noting his past efforts in the legislature and the courts. In response to the same question, Mr. Jealous wrote, “I believe that Maryland should lead the fight on redistricting reform in a fair and non-partisan manner that does not indefinitely hand control of the House of Representatives to Republicans. Redistricting compacts such as the one passed by the Maryland legislature and vetoed by Gov. Hogan are a fair and equitable solution to increase the accountability of Congress to the voters and reduce gerrymandering.”

In other words, Mr. Jealous’ commitment to the principle is overriden by his partisan interests.

But he of all people should recognize that you don’t change the national norm by failing to lead by example. That’s precisely the argument he made several years ago in leading the effort to abolish the death penalty in Maryland. Doing so would make relatively little practical difference, given how few people were sentenced to death here compared to states like Texas, Florida and Virginia. But, he argued, outlawing capital punishment here would make it a little easier to do it in the next state, and the next one after that until the few states that account for most death sentences become real outliers. Then, the dynamics of a court challenge to the practice would be altogether different. He was quite persuasive on the point.

The same is true of redistricting. Fairly drawn district lines in Maryland might swing a seat or two to the Republicans, but the impact is minor compared to what would happen if the lines were drawn fairly in Texas or North Carolina. But it’s going to take real leadership, the courageous kind that risks something for a larger goal, to achieve that. We won’t get to the right place by doing the wrong thing.