(CNN) The showdown between President Donald Trump and former FBI Director James Comey reignited this week with the publication of excerpts from Comey's forthcoming tell-all book.

While a recent ABC News/Washington Post poll shows that Comey is better liked and trusted than Trump, that public perception of the two men actually hasn't changed since last May, when Trump fired Comey.

At the heart of this lack of variation in polls over time is that the issue of Comey vs. Trump has become purely partisan, making it difficult to get people to change opinions once they're locked into their political tribe.

We can look specifically at the question of whether Americans approved of Trump's decision to fire Comey to see how each side is staying its political corner. In the latest ABC News/Washington Post poll , only 11% of Democrats approve of Trump's decision to fire Comey compared with 70% of Republicans. In a Monmouth University poll last May, the numbers were nearly identical with 10% of Democrats approving of Trump's to fire Comey compared with 74% of Republicans.

That partisan split creates an overall picture today of 14 percentage points more Americans disapproving (47%) than approving (33%) of Trump's decision to fire Comey. In an average of May polls from last year, 12 percentage points more of Americans disapproved than approved of the decision to fire Comey.

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