At the behest of Donald Trump, the state is pushing to restructure congressional maps to add as many as five seats for Republicans

At the insistence of Donald Trump, Republicans in Texas are pushing ahead with an effort to redraw their congressional map to pick up as many as five additional Republican seats.

The decision has set off a cascading legal battle. State lawmakers have fled Texas as part of an effort to stop Republicans from passing the map. Democrats in other states have said they will retaliate, setting the stage for a nasty and prolonged redistricting tit-for-tat that could last for years.

After a nationwide census every 10 years, all 50 US states are required to redraw their congressional districts to account for population shifts. The US constitution entrusts the power to draw congressional lines to the state legislatures in each state. Since the 18th century, politicians have tried to use this line-drawing power to punish their political rivals. In the 19th century, the practice of manipulating district lines for political lines became known as gerrymandering.

While states are required to redistrict every 10 years, the constitution contains no explicit ban on redrawing boundaries before the decade is up.