A 58-year-old man presents with several months of progressive exertional dyspnea and intermittent substernal chest pressure. He reports a remote history of a painless genital ulcer in his 20s that resolved without treatment. He has had no regular medical care. Vital signs show BP 168/92 mm Hg and HR 92/min. Cardiac exam reveals an early diastolic decrescendo murmur best heard at the left sternal border. Chest X-ray shows widening of the mediastinum with linear calcifications of the aortic arch. CT angiography demonstrates a 6.7-cm aneurysmal dilation of the ascending thoracic aorta.

Which of the following best explains the underlying pathogenesis of this patient’s condition?