Citizens United
The argument made and accepted by the court in the case Citizens United v. Federal Election Commission, 558 U.S. 310 (2010) was specifically that a total bar on corporate electioneering communications, and a bar of money spent to produce or distribute such communications was unconstitutional. Money so spent was deemed a way of creating and distributing speech, and thus equally protected with speech itself. There was no holding that spending in general is to be equated with speech in general.
Specifically in the majority opinion, the Court wrote:
Section 441b’s prohibition on corporate independent expenditures is thus a ban on speech. As a “restriction on the amount of money a person or group can spend on political communication during a campaign,” that statute “necessarily reduces the quantity of expression by restricting the number of issues discussed, the depth of their exploration, and the size of the audience reached.” Buckley v. Valeo, 424 U. S. 1, 19 (1976) (per curiam). Were the Court to uphold these restrictions, the Government could repress speech by silencing certain voices at any of the various points in the speech process. See McConnell, supra, at 251 (opinion of Scalia, J.) (Government could repress speech by “attacking all levels of the production and dissemination of ideas,” for “effective public communication requires the speaker to make use of the services of others”). If §441b applied to individuals, no one would believe that it is merely a time, place, or manner restriction on speech. Its purpose and effect are to silence entities whose voices the Government deems to be suspect.
Speech is an essential mechanism of democracy, for it is the means to hold officials accountable to the people. See Buckley, supra, at 14–15 (“In a republic where the people are sovereign, the ability of the citizenry to make informed choices among candidates for office is essential”). The right of citizens to inquire, to hear, to speak, and to use information to reach consensus is a precondition to enlightened self-government and a necessary means to protect it. The First Amendment “ ‘has its fullest and most urgent application’ to speech uttered during a campaign for political office.” Eu v. San Francisco County Democratic Central Comm., 489 U. S. 214, 223 (1989) (quoting Monitor Patriot Co. v. Roy, 401 U. S. 265, 272 (1971)); see Buckley, supra, at 14 (“Discussion of public issues and debate on the qualifications of candidates are integral to the operation of the system of government established by our Constitution”).
Thus nothing in Citizens United held or suggests that an embargo or a travel restriction was equivalent to a ban on speech, or was otherwise unconstitutional
Travel Restrictions
The general concept of travel restrictions, primarily as connected with the COVID-19 pandemic, was discussed in "The right to Travel and National Quarantines: Coronavirus Tests the Limits" from Georgetown Law by Meryl Justin Chertoff, Executive Director of the Georgetown Project on State and Local Government Policy and Law.
There have been a number of cases on travel restrictions in US law, having nothing to do with spending or free speech.
In Edwards v. People of State of California, 314 U.S. 160 (1941) The US Supreme Court ruled that California could not prohibit the entry of indigent people from other states. The opinion dealt primarily with the limitations that the Intestate Commerce Clause of the Federal Constitution places on the states, and secondarily with discussion of nineteenth-century cases allowing limits on the movement of "paupers" based on "theory of the Elizabethan poor laws". In particular City of New York v. Miln, 11 Pet. 102 (1837), and cases citing it, was declared no longer good law on this point.
However, a concurring opinion by Justices Douglas joined by Justices Black and Murphy, and another by Justice Jackson held that the right to travel from one state of the US to another was protected by the Privileges and Immunities clause of the Fourteenth Amendment.
Justice Douglas wrote:
I am of the opinion that the right of persons to move freely from State to State occupies a more protected position in our constitutional system than does the movement of cattle, fruit, steel and coal across state lines. While the opinion of the Court expresses no view on that issue, the right involved is so fundamental that I deem it appropriate to indicate the reach of the constitutional question which is present. The right to move freely from State to State is an incident of national citizenship protected by the privileges and immunities clause of the Fourteenth Amendment against state interference ... Now it is apparent that this right is not specifically granted by the Constitution. Yet before the Fourteenth Amendment it was recognized as a right fundamental to the national character of our Federal government. It was so decided in 1867 by Crandall v. Nevada, 6 Wall. 35, 39. In that case this Court struck down a Nevada tax 'upon every person leaving the State' by common carrier. Mr. Justice Miller writing for the Court held that the right to move freely throughout the nation was a right of national citizenship. That the right was implied did not make it any the less 'guaranteed' by the Constitution. Id., 6 Wall. page 47.
That case, of course, dealt only with travel within the US.
In Speaker v. U.S. D. H. S, 623 F.3d 1371 (11th Cir. 2010) the 11th Circuit Court of Appeals mentions without disapproval an order prohibiting a person who had been in an area with recent smallpox cases to fly by commercial carrier into the US, although that case was actually about alleged violations of the Privacy Act in regard to the ensuing publicity.
