This issue predates Trump and will last well beyond him. That much is clear. But there are still at least two massive flaws in cassa's attempt to pin the blame instead on the Democrats for resisting his policies. Firstly, as I have already pointed out, it is not the Democrats who have cut, or tried to cut, US funding for the countries of origin of these people and the many other migrants who try the same journey. That's on the current administration, and it will only serve to exacerbate the wider issue.
Secondly, when Obama was President, and even more so when Bush was president, the numbers of people crossing or attempting to cross the US border were on a long-term and significant decline (save for a bump in around 2014). Both parties were more or less cooperating in that time to deal with the issue and invest greater resources, and it was paying off. Democrats do care about border security, and even now the Democrat-controlled lower House has passed several large bills that would provide plenty of funding for increased security, including one only this week:
https://edition.cnn.com/2019/06/25/politics/house-vote-border-funding/index.html
This latest bill still has to pass through the Senate and Donald Trump, and hopefully that will happen very soon.
Thirdly, there's a context to the Democrat blocking of Trump that cassa's either ignoring or didn't appreciate, which is that Republicans basically spent the last two years of Obama's presidency blocking virtually everything he did or tried to do. Most notably that included trying, and failing, to destroy his Healthcare Act, refusing on dubious grounds to even let his Supreme Court nominee get near the Senate, and the last few Congresses of Obama's term were some of the least productive in terms of major legislation in US History. All of this has been conveniently ignored by Republicans and Trump supporters, who should not be surprised at the idea that Democrats are playing the same sorts of dirty trick as much as they can, and even more so now that Democrats have control of the House of Representatives. No doubt they are doing their best to stop Trump as much as possible, but in that regard it is no different from what Republicans were doing in Obama's term.
Yes, I disagree with much of Trump's approach. I find the rhetoric of "Mexico are sending us their rapists... some, I assume, are good people" more than a little distasteful. The fixation with a border wall, too -- completely unnecessary, when dropping that fixation would allow an easy compromise to be met more or less the next day that both parties would agree to. I do my best not to let that colour my view of latest developments, and probably fail from time to time. But in blaming Democrats for this, he, and cassa, are both wrong.