If an elected official makes a bad decision, they deserve criticism for their action. That is the prime reason democracy works and makes government as efficient and productive as it can be. When officials are allowed to take action with no repercussions from their constituents, they often abuse their power. These decisions need to be examined and appropriately criticized when the situation calls for scorn.
It is perfectly okay, and more than acceptable, that elected officials such as the president be maligned. However, the scope of such criticism should be limited to the elected officials performance in office. Personal attacks on the official or his family should be completely off-limits. Criticism comes with the territory. If you can't take the heat get out of the kitchen.
Yes, it is okay to speak about the President in a critical manner. Freedom of Speech is a crucial right in a free and democratic society. Most speech, even negative speech needs to be protected for people to have discussion and debate. If people weren't allowed to speak ill about the President, voices and opinions would be shut out. Only one opinion would be able to rule, and that is called tyranny.
Yes, it is okay to malign elected officials such as the President because one of the major tenets of democracy is free speech. Citizens have the right to malign the president if they feel like his actions are not in accordance with the principles of the nation. What makes America different from other countries is free speech, and that should never be compromised.