The reason why Python base environment is unable to import Tensorflow is that Anaconda does not store the tensorflow package in the base environment.
create a new separate environment in Anaconda dedicated to TensorFlow as follows:
conda create -n newenvt anaconda python=python_version
replace python_version by your python version
activate the new environment as follows:
activate newenvt
Then install tensorflow into the new environment (newenvt) as follows:
conda install tensorflow
Now you can check it by issuing the following python code and it will work fine.
import tensorflow