Delhi Chief Minister Arvind Kejriwal said on Friday that Congress Vice President Rahul Gandhi had no courage to expose Prime Minister Narendra Modi's alleged corruption."Rahul doesn't have guts to expose anything against Modiji. The day he does it, Modiji will arrest (his brother-in-law) Robert Vadra," the Aam Aadmi Party leader tweeted.Kejriwal's comment came days after Gandhi threatened to expose corruption by Modi. He has not done so, but on Friday he led a Congress delegation to Modi to plead the cause of the farmers.