Lincoln’s Peoria Speech was delivered in October 1854, when Lincoln was a Whig, not Republican.
Lincoln did not certainly become Republican until the 1856 elections.
The reason Whigs were replaced by Republicans can be boiled down to one word: abolition.
All of which we can be certain D’Souza knows and Democrats like jeffersondem are loathe to admit.
The problem for you here is neither Lincoln nor the VAST majority of Republicans were abolitionists.
Your argument fails.
NOT!!
100% of Republicans in that day favored abolition in their own states, though very few wanted to override the Constitution's recognition of slavery in the South.
And Lincoln's abolitionist credentials were certified early on by his support for a plan of compensated emancipation in Union slave-states.