downplayer

[daʊn'pleɪ]
vt.
[美国口语]缩小(某事的重要性、价值、力量等)，小看，轻视，降低，故意贬低…重要性，低估；对…轻描淡写；降低调子陈述；减弱：
The press has downplayed the president's role in the foreign affairs.
报界贬低了总统在外交事务中所起的作用。