My experience of "To crack the whip" in Oz is that it means to exert pressure on a person or group to achieve a goal desired by the one cracking the whip. "Fair crack of the whip" can be used as a riposte to the whip cracker by the one(s) being pressured; it is almost the equivalent of "Fair go, mate."

As it happens, whip makers among us would also know that the short and extremely flexible attachment to the end of the fall of the whip (ie., the bit that exceeds Mach 1 when the whip is cracked, thus making the "crack") is called the "whip cracker".

I'm a little surprised that "the mark" featured in US usage,as I've always thought of "toeing the line" as associated with boxing (and thus common wherever it featured as an activity) whereas I'd thought of "Stepping up to the mark" as associated with archery and common in British usage but less so in US usage.

I learn something every day.

Cheers, Rowan