Via TRAC:

The latest available data from the federal courts show that during December 2018 the government reported 37 new federal civil immigration naturalization lawsuits. According to the case-by-case information analyzed by the Transactional Records Access Clearinghouse (TRAC) at Syracuse University, this number is up 26% over the last six months. This continues an upward monthly trend in naturalization litigation evident since March 2017 after President Trump assumed office - a trend that has accelerated over the last six months.

During calendar year 2018 the government reported 380 federal civil immigration naturalization lawsuits. This marked the highest annual total since the 2008-2009 period. See previous TRAC report on earlier trends.