(This measure has not been amended since it was introduced. The summary has been expanded because action occurred on the measure.) Securing the Cities Act of 2017 (Sec. 2) This bill amends the Homeland Security Act of 2002 to require the Domestic Nuclear Detection Office (DNDO) to establish the Securing the Cities program to enhance the ability of the United States to detect and prevent terrorist attacks and other high consequence events utilizing nuclear or other radiological materials that pose a high risk to homeland security in high-risk urban areas. Under such program, the DNDO shall: assist state, local, tribal, and territorial governments in designing and implementing, or enhancing existing, architectures for coordinated and integrated detection and interdiction of nuclear or other radiological materials that are out of regulatory control; support the development of a region-wide operating capability to detect and report on nuclear and other radioactive materials out of regulatory control; provide resources to enhance detection, analysis, communication, and coordination to better integrate state, local, tribal, and territorial assets into federal operations; facilitate alarm adjudication and provide subject matter expertise and technical assistance on concepts of operations, training, exercises, and alarm response protocols; communicate with, and promote sharing of information about the presence or detection of nuclear or other radiological materials among, appropriate federal, state, local, tribal, and territorial governments in a manner that ensures transparency; provide augmenting resources to enable state, local, tribal, and territorial governments to sustain and refresh their capabilities developed under the program; and designate participating jurisdictions from among high-risk urban areas and other cities and regions, as appropriate, and notify Congress at least three days before designating or changing such jurisdictions. The Comptroller General is required to submit an assessment evaluating the effectiveness of the program. (Sec. 3) The DNDO shall report to Congress on the feasibility of developing model exercises to test the preparedness of jurisdictions participating in the program in meeting the challenges that may be posed by a range of nuclear and radiological threats.