When it became apparent that Alexei was a hemophiliac why didn’t Nicholas overturn the Pauline succession laws and reinstated Peter the Great’s succession law which allowed the czar to appoint his own successor?
A czar’s power and authority is absolute so why wasn’t this an option for Nicholas?
There's always more to be said, but you may be interested in my answers to Why didn't Tsar Nicholas II of Russia change the rules of succession so that women were allowed to inherit the throne? as well as Why did Tsar Nicolas the II keep information regarding his sons illness private?