Last week about 23 percent of eligible Maryland voters cast ballots in the cantankerous gubernatorial primary — the lowest rate in at least 24 years, if not longer.

The low turnout is being blamed on a number of things, but on the top of that list is the decision of Maryland lawmakers to bump the gubernatorial primary from September to June so that election officials would have more time to prepare general election ballots to send to troops serving overseas. There are also worries that voters just don’t care enough.

Scott Clement, a pollster here at The Washington Post, pulled together stats from the past seven gubernatorial primaries, which The Post’s Denise Lu assembled into these four graphs that show the gradual decline of gubernatorial primary participation for Democrats and Republicans over the past two dozen years. (For each primary, Scott focused on whichever statewide race had the most votes, which was sometimes a race for U.S. Senate instead of governor. And if you are having trouble remembering who ran in which year, scroll down for a cheat sheet.)

Who ran when?

1990: In the Democratic primary, then-Gov. William Donald Schaefer won with 78 percent of the vote. In the GOP primary, William S. Shepard won with 53 percent. Schaefer, who was first elected governor in 1986, was elected to a second term that year.

1994: In the Democratic primary, Parris N. Glendening won with 54 percent of the vote. Ellen R. Sauerbrey became the GOP nominee with 52 percent of the vote. Glendening became governor.

1998: Glendening ran for a second term, getting 70 percent of Democratic primary votes. He again faced Sauerbrey in the general election and won.

2002: Kathleen Kennedy Townsend won the Democratic nomination with 80 percent of the vote. The GOP nominee was Robert L. Ehrlich Jr., who got nearly 93 percent of Republican primary votes. Ehrlich went on to win the close general election, becoming Maryland’s first Republican governor since Spiro Agnew in the 1960s.

2006: Ehrlich ran for a second term and easily won his primary. In the Democratic primary, Martin O’Malley faced Montgomery County Executive Doug Duncan, who dropped out of the race months before the primary, leaving O’Malley unopposed. O’Malley then beat Ehrlich in the general election. But the most-watched primary that year was a close race for the U.S. Senate: In the GOP primary, Michael S. Steele won with 87 percent of the votes, while Benjamin L. Cardin won the Democratic primary with nearly 44 percent. Cardin went on to win the seat.

2010: O’Malley ran for reelection and won with 86 percent of Democrat’s votes. Ehrlich tried to get his job back, winning his primary with more than 75 percent of the vote but then losing the general election to O’Malley.

2014: With O’Malley being term-limited out of office, Lt. Gov. Anthony G. Brown announced that he would run for governor. Brown faced Attorney General Douglas F. Gansler and Del. Heather R. Mizeur (Montgomery) in one of the nastiest Democratic primaries in decades. Brown won on June 24 with more than half of votes. In the November general election, Brown will face Larry Hogan, an Anne Arundel County businessman who served in the Ehrlich Administration. Hogan won the GOP nomination with 43 percent of votes.