Gerrymandering is the process of redrawing electoral districts to benefit one political party. By redrawing the districts, the politicians can create districts that will vote for their party, even if the opposing party wins a majority of the votes in the state, thus undermining the entire democratic process.
Republicans and gerrymandering
In the 2012 U.S. Presidential Election, in addition to rejecting the crazy ideas of Mitt Romney, American voters also decided to put the Democrats back in control of the U.S. House of Representatives, because Republicans had control for the previous two years, and there is nothing positive to say about their reign. However thanks to gerrymandering, despite the fact that Democratic candidates got more votes overall, Republicans kept control and for at least two more years will fight against a great deal that will improve the United States. A similar thing happened in 1996, when the Democrats won the popular vote to win back the house, but Republicans preveted Americans having their voices heard through gerrymandering. This is why we need democracy, otherwise we have to face Republicans. It's not like this is the first time they've pulled off something like this.
They Admitted It!
In January of 2013, a memo entitled, "How a Strategy of Targeting State Legislative Races in 2010 Led to a Republican U.S. House Majority in 2013," was released. It claimed that regaining state legislatures in 2010 allowed them to keep the House in 2012. So, my friends, in the year 2020, go to the polls, and elect democrats to state general assemblies. 
Republicans and voter suppression
Voter suppression means making it hard for people to vote or threatening them with dire consequences if the candidate you dislike wins. The ACLU complains Republicans are making it hard for African-Americans, disabled voters, older voters and students. These are all citizens likely to vote Democrat.