[Python] python else statement causes a continuous loop

Not understanding why my Python else statement is causing an infinite loop?

m = 0
while m < len(dataframe):
if dataframe['firstname'].iloc[m] == 'Donald':
dataframe.loc[m, 'lastname'] = 'Trump'
elif dataframe['firstname'].iloc[m] == 'Joe':
dataframe.loc[m, 'lastname'] = 'Biden'
elif dataframe['firstname'].iloc[m] == 'Barrack':
dataframe.loc[m, 'lastname'] = 'Obama'
else:
dataframe.loc[m, 'lastname'] = 'last name does not matter'

m+=1

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