The visitor’s first goal came from a corner after goalkeeper Liam Roberts dropped the ball and allowed Ben Tozer to tap home from close range.
After a Josh Gordon penalty got the Saddlers back in the game, Liam Kinsella then sold Alfie Bates short with a poor pass and allowed Cheltenham to break in numbers - resulting in striker Luke Varney slotting home.
But Clarke says he takes responsibility for the bad run of form, as Walsall have now lost three games on the bounce.
“You don’t need me preaching again this week, it’s not good enough,” he said.
“Mentality, poor, maybe four or five did themselves sort of justice.
“Poor from us, but I take full responsbility, we’re miles away from being a successful team in League Two.
“Miles away, let’s not beat around the bush.
“There’s a fear factor at home at the minute, I understand that, I don’t blame the fans for that.
“I blame myself for that because the mentality of the players is something I touch on all the time.
“When the chips are down, we chuck them a goal don’t we.
“Last thing you need to do when you’re on a bad run at home, backs are against the wall, you score a goal and then you give them another sloppy goal.
“We’re killing ourselves.”