As investment experts squabble over the triggers for the sharp slide in global equity markets this month, business strategists at local banks will be attuned to the political scenarios that could flow later this year from the spike in global bond yields.It now seems the case that the cost of replenishing the major banks' funding programs bottomed around September last year.Interest rate rises have a tendency to intensify relations between governing politicians and bankers, especially when the latter see fit to increase the cost of loans outside of the Reserve Bank's official movements.Banks are facing a slowdown in lending growth this year, which will entice their managements to rebuild net interest margins to maintain earnings momentum.If the Reserve Bank decides to delay raising official rates to shield the country's debt-laden household sector from the perils of a protracted property market correction, the major banks might be tempted to hike pricing on mortgages and other loans without the imprimatur of an official move.Such a development looms as a political challenge for the industry.Not only would it coincide with the potentially damaging hearings of the Hayne Royal Commission, but it would also come as the Turnbull Government enters the prefatory stages of an unusual election season in 2019.If the government decides to run its full term until the end of August next year, it still faces a half-Senate election that must be held by the middle of May.John Howard boosted his majority in 2001 when the RBA board lowered the cash rate twice in the three monthly meetings ahead of the national election that year.Six years later he was swept out of government when official rates were hiked at two of the four central bank meetings preceding his final election.A bottom line of electoral marketplaces is that interest rate movements matter.It's stating the obvious that their importance is magnified when a record number of voters are saddled with record-sized mortgages and other debts.However, it will not be easy for the banks to shirk the reality that the industry's average net interest margin is touching a 25 year low of 201 basis points.With a net interest margin of only 188 basis points, National Australia Bank is under the most pressure of the four majors because of its disproportionate reliance on wholesale funding.The turning of the yield curve is occurring at an awkward moment for Australian bankers and potentially sets them on another collision course with the nation's elected officials.