“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.
The First Amendment ensures freedom from government intrusion of freedom of speech, freedom of religious belief, freedom of the press, and freedom of petition and assembly. These protections apply only to government laws and actions that restrict such freedoms, not to actions by private citizens or entities.
As Oliver Wendell Holmes said, the First Amendment is premised on a free market of ideas. It ensures that the government does not get to control the truth by asserting control over the media or by suppressing protest, which is what happens in many other countries (such as Russia, China and countries in the Middle East) that do not share the principles, freedoms and beliefs reflected in the US Constitution.
Throughout American history, in a large number of cases, the courts have generally interpreted the First Amendment broadly, including carving out the freedom to do or say vile and abhorrent things to ensure that all Americans are kept free, including minorities and people with extremely unpopular views. (see TX v. Johnson). Since, at some point in a person's life, anyone can potentially be a minority or hold a minority view, protecting such vile views means that all US citizens are more free to have and express their own beliefs without being persecuted by the government.
The First Amendment has also been interpreted to require a very high degree of media freedom from government influence (NY Times v. US, no “prior restraint” – government not permitted to preempt what the media plans to publish). Laws that sought to restrict the criticism of the government have also been struck down as unconstitutional (NY v Sullivan).
It is a common assumption – including based on media coverage of abortion and other social issues – that the Supreme Court is entirely a partisan political institution. Although all humans are influenced by their politics and ideologies, Supreme Court justices adhere to the Constitution, law and precedent. In some cases, interpretations of core First Amendment freedoms may not be partisan at all, and conservatives have sometimes been more vigorous defenders than liberals. When free speech is attacked, conservatives and liberals alike on the Supreme Court should be expected to uphold the Constitution and precedent, and not just line up on a partisan basis. (see US v Nixon, unanimous court – liberals and conservatives - required production of the Nixon tapes).
On January 20, 2017, Donald Trump will take the following oath of office, found in Article II of the Constitution:
“I do solemnly swear (or affirm) that I will faithfully execute the office of the of the President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States.”
At that moment, he will no longer merely be a citizen; rather, he will be responsible as President for upholding the Constitution, including the First Amendment.
President-elect Trump has threatened to seek to change the libel laws to make it easier to bring lawsuits against the press. This doesn't make much sense, as there is no federal libel law (each state has it's own libel law...), and in any event, any such attempts would be subject to the limits of the First Amendment (which requires a heightened "actual malice" standard to prove libel against public officials - see NY Times v. Sullivan).
Short of talking about hypothetical laws that violate the First Amendment, perhaps a more important question will be: what will President Trump's role be in the free market of ideas? With the rise of social media, and his expertise at using it, President Trump has his own media platform - Twitter - and he essentially has the loudest voice.
President Trump's use of Twitter may create new risks to, and legal interpretations of, the First Amendment. He is likely to take the position that his Tweets are merely his personal opinion, rather than the type of "state action" needed to trigger the First Amendment. He has also used Twitter to engage in pointed attacks on media outlets - i.e. the "failing NY Times". We will see if the law is interpreted to permit him the freedom to direct negative Tweets at those who oppose him, and to direct attacks on media outlets that critique him. But as the lead custodian of the Constitution, should he do so?