def METHOD_NAME(
    df: pd.DataFrame, datetime_column: str, td: timedelta
) -> pd.DataFrame:
    """
    Takes a ``pandas.DataFrame`` containing a column of ``datetime`` dtype, shifts all
    values of the datetime column by ``-td`` and return the modified dataframe, all other
    columns untouched.
    """
    df = df.copy(deep=True)
    df[datetime_column] = df[datetime_column] - td
    return df