The Carter Administration did impose strict rules and regulations to discourage illegal immigration. Employers were required to obtain three documents verifying citizenship and residency from every new hire and it was illegal to hire anybody who could not produce such documentation. There were stiff penalties for breaking the rules.
It was pretty effective but tedious for employers at first, most especially those who hired day workers or had to put somebody to work immediately. So they fudged a bit after awhile and then more and more assuming they could get the documentation after the fact. And because the rules were poorly enforced pretty soon everybody, including the government forgot about them.
Then Reagan agreed to amnesty for the 3 million illegals in the country at that time on condition that Congress would ensure that no more would be admitted other than through legal means and the rules regulating those legal means were tough and difficult. But his most Democrat controlled Congress wasn't eager to help with that a whole lot even though they were the old style Democrats and not the woke/progressive/Marxist minded Democrats we have in Congress now.
Every President since has tried to enforce immigration & illegal immigration laws, including Obama who still admitted far more than was technically legal to do so. But the caravans kept coming in my opinion funded by Marxist minded people who intend to overtake the USA.
Trump effectively stopped the caravans by coercing Mexico to put troops on their southern border to stop them. And he allowed the CBP and ICE to do their jobs and his border wall, even though he didn't get to complete it, was very helpful to them in doing their jobs. Illegal immigration slowed to a trickle.
Biden reversed all that and now we have millions upon millions more undocumented people who have no legal right to be here and 10,000 to 13,000 arriving at the southern border every day. If Biden continues to refuse to act, by the end of next year he will have admitted at least more than 10 to 15 million or more illegals and that doesn't count at least hundreds of thousands of 'gottaways' that we have no idea who they are or where they are or what their intentions are.
Many in the position to know say it is the most serious threat to American security since 9/11.