Socialism is, in the de facto sense, the government putting a gun to your head and demanding a large portion of your labor and possessions (e.g., "money") and if you don't give it over then you face losing all your money and all your possessions and may even face a stiff prison sentence--in other words, a form of slavery.
You have no say so in what the government does with that money and the money that you are forced to give may or may not make it to the people who need it. Anytime a middle man (i.e., government) is used to administrate the funds, the bureaucracy itself becomes parasitic to the extent that a large part of those funds never make it to people in need in order to feed the burgeoning bureaucracy.
However, in the de jure sense, the social security system/administration and social security number in the US are "voluntary" in order to comply with the 13th amendment (no involuntary servitude or slavery). However, in real life one is required to have a social security number to obtain a bank account, credit/debit cards as well as an ID, driver's license, business license, professional license, fishing/hunting license, etc, under US Code, Title 42, Section 666.
BTW, I have letters from the Social Security Administration that reveal that it is a corporation (created by Congress without constitutional authority) under the jurisdiction of another corporation called the IRS. (The SSA does not even have franking privileges under the US Constitution as evidenced by the postage paid on the envelope.)
I would venture to say that it is pretty much the same in most countries in the world.
If, as Dennis says in the OP, Trump said that the US will never be socialist, I'm guessing he either doesn't have a clue about what socialism is or perhaps he was thinking to himself, well, it's really more fascist than socialist.
Even taxation is a socialist principle. In spite of what Ben Franklin wrote, taxation is entirely unnecessary in that the US could take over the Federal Reserve and banking industry and use the interest that people pay on loans, etc, to fund public necessities. Theoretically, any country could take over the banking industry and fund roads, bridges, etc, and perhaps even social programs thus eliminating the need for "socialism".