It "oscillates" but the overall movement is in one direction.

Open borders is an easy policy to implement. Open the border, put zero effort into enforcement, let people stream over. Closing the border and deportations is work. Trump will probably have deported maybe 5%-10% of the illegals the Democrats let in. Eventually there will be an "amnesty", perhaps as soon as 2029. Even if there is no amnesty, the children of illegal immigrants get birthright citizenship. These are all future Democrat voters.

Democrats, when they're in power, create a whole bunch of new bad laws and policies. "Conservatives", when they're in power, reverse maybe 5%-10% of the new bad laws and call it a victory. The net effect is an erosion of freedom and move towards communism (or worse, Sharia Law).

Great Replacement is a winning issue. Import new voters, it's easier to win elections, so they can import even more new voters. Their end goal is to be like the ANC in South Africa, where they can't be voted out no matter how badly they screw up.

Most people on the right have jobs and families, which means any sort of aggressive counter-action comes at great personal risk.