Let's get something straight. There was no "Mexico" prior to Spanish colonization. There were Indian empires in southern and mid-Mexico, but those empires did not range in to what is now the U.S.
The Spanish occupied these Indian empires plus what is now the western U.S. from ~1500 til Mexican independence (declared 16 Sep 1810 and won several years later).
Therefore, the nation of Mexico occupied those lands that are now part of the U.S. for a maximum of 38 years before they were ceded to the U.S. in the aftermath of the Mexican War.
To claim that 38 years of occupation (and there was virtually no Mexican presence in these lands) trumps the U.S. occupation of almost 160 years is absurd.
And, if length of occupation is the benchmark, then the flag of Spain should be flying there.
To claim the current invasion as 're-colonization' is stretching it as well. At least in California. Mexico never had more than minimal control over this state, and when the time to succeed came, most mexican citizens embraced the California Republic with both arms.