There are both issues and problems which hurt and benefit opposing parties at the same time, Republicans ignoring those won't help their cause, in the same manner democrats won't get any support from ignoring the border situation.
Democrats are very clever. Illegal immigrants are not just "immigrants". They are invaders shipped in by the Democrat Party to increase their vote base. And that is exactly the reason why the states along the border (Arizona, Nevada, Texas.etc) has seen a rapid decrease in support for the Dems. Now the Democrats wants to include illegal aliens in census, so that they can inflate the population in deep-blue states such as California and thereby increase the number of House seats there.
Illegal Immigrants cannot vote in elections, though. Not even legal immigrants can, only citizens. I have seen hosts in Fox claiming the democrat party want to grant immigrants the ability to vote in November, but that is non-sense, since it would be illegal to do so.
It would make more sense in all the immigration going on in the United States had a different objective which did not necessarily involved the elections. For example, we could argue the influx of immigrants is very advantageous for companies and associations which seek to especulate with the value of real state and the renting of living spaces.
With more people in the USA, the demand will only go up for living places, do the landlords can ask for more money. That makes more sense than seeking directly to alter the voting population of the USA by November. Not even mention the access to cheap labor big companies expect from immigrants.