The Marines have survived such threats to its existence in the past. After the end of World War II, Congress settled on the USMC having three divisions and three air wings, although the 3rd MarDiv and 1st MAW, both based on Okinawa, are nominally manned by units temporarily deployed from the other two divisions and wings.
The Marines are very smooth politicians, and have clout on The Hill. In just recent years, they have gotten almost everything they wanted; especially on the aviation side. They got the very controversial MV-22 Osprey and F-35B fighter jet, the AH-1Z, the UH-1Y, the C-130J, and the CH-53K will soon fly as a test aircraft. These aircraft were in various planning stages before the GWOT began, but the aircraft replacements have exclusively occurred in the last 10 years.
Hell, the entire U.S. military is bloated and needs to be reduced. Russia and China are the only countries which can really threaten us (with nukes, mostly), and neither has the ability to project power beyond their immediate regions (except for launching intercontinental nukes). All other "threats" to U.S. security are small players who are used as an excuse to sustain the empire. The world would be much safer overall if U.S. militarism did not exist.