You need insurance for your car that's valid in the USA. And it's not the usual minimum amounts.
C. Insurance Policy
For events with public road transit sections, the owner/entrant must
warrant having a valid auto insurance policy with liability limits of not less
than $100,000/$200,000/$50,000 in force for each vehicle entered (this
includes support vehicles). Actual proof of such insurance showing limits
must be produced to event officials at registration.
A warrant of insurance (included on official entry form) must be signed by
the vehicle owner which states, “I warrant the competition vehicle has
current minimum insurance coverage of $100,000/$200,000/$50,000
which meets or exceeds the vehicle insurance standards established and
required by Rally America.” Rally vehicles without the required
documents will not be allowed to start the event.
4.4. PROOF OF INSURANCE
Proof of insurance for the competition vehicle must be presented before the
start of the event. Proof of insurance consists of a policy declaration form
that lists one or more named insured individuals, one or more vehicles
covered by the policy and the limits of coverage. The declaration must list
either the entered driver or entered vehicle or both. If the entered driver is
not listed as the named insured, permission of use from the named insured is
required. If the vehicle is not listed as an insured vehicle, proof of ownership
is required and, if the driver is not the owner, permission of use from the
owner is required. If both the driver and the vehicle are listed, no additional
documentation is required for proof of insurance.
Proof of ownership can be either the title/ownership certificate or current
vehicle registration listing the registered owner. Permission of use can be an
authorization statement made directly to the registrar or an authorization
letter.
Proof of insurance for support vehicles (such as service trucks) must also be
presented before the start of the event. Proof of insurance consists of a
policy declaration form as above. Either one of the named insured on the
policy must be the entered driver, co-driver or a registered member of the
crew or permission of use for the support vehicle (as described above) is
required. In lieu of an insurance policy declaration, a rental agreement for
the vehicle is acceptable.