There are growing signs that veteran Rep. Darrell Issa, R-Vista, could be headed for an election dogfight.

Issa has breezed to re-election seven times since taking office in 2001, but the landscape is different this time.

His support for Donald Trump could undermine this year’s bid. The Republican edge in his two-county district’s voter registration is shrinking. And his Democratic opponent’s background as a Marine colonel holds particular appeal in a district that includes and surrounds Camp Pendleton.

In the 2012 and 2014 primaries, Issa prevailed by at least 30 percentage points. In June, he beat Democrat Doug Applegate by a relatively modest 5.3 percentage points. That’s less than the GOP’s 8.4-point advantage in voter registration – an advantage that has shrunk from 10.7 points since the beginning of the year.