This is true. Both the Canadian and US legal systems are underpinned by centuries of British Common Law. Libel (untrue written statements) and slander (verbal) laws protects against things which are demonstrably untrue (i.e. objective or quantitative statements refuted by facts), but the individual or group(s) alleging slander must file the lawsuit, and they have to show harm, and they must prove the defendant knew what was being said was untrue (i.e ‘duty - breach - cause - harm’).
A politician is the quintessential public figure.
The First Amendment's guarantee of free speech is at its maximum when political speech is aimed at politicians and public officers.
So much so that the First Amendment's Freedom of Speech Clause protects mendacious political candidates who lie about other political candidates.
The Free Speech Clause also protects unrelenting vituperation, exaggerative vilification, and venomous denouncement of politicians and public officers.
"Politics ain't beanbag."
In
Rickert v. Washington (2007), the Washington Supreme Court struck down a state law that punished candidates for political office who knowingly made "a false statement of material fact about a candidate for public office."
The Court found that “The notion that the government, rather than the people, may be the final arbiter of truth in political debate is fundamentally at odds with the First Amendment" and that the law "naively assumes that the government is capable of correctly and consistently negotiating the thin line between fact and opinion in political speech."